Introduction to Programming and Computer Science - Full Course

Introduction to Programming and Computer Science - Full Course

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Welcome to Introduction To Programming. My name is Steven And my name is Sean. Over the next 90 minutes, we’ll be taking you through this series consisting of 21 different segments that hope to cover the basics of computer programming, which can apply to any and all programming languages you might want to learn. We’ll be starting with the simplest question of what is programming, and from there will be working our way up as we talk about common features of computer science such as loops and arrays. We’ll discuss how to read and write code, debug code you’ve written, some strategies to help plan out your code, and much, much more. The complete list of topics that are going to be covered in this lecture-style video are shown on the screen now. Additionally, there will be time-stamps in the description, so feel free to skip around if you are already proficient in some areas of computer science, or just want to know about a specific topic we will be covering. Hopefully, by the end of the series, you’ll have a basic understanding of what computer science is, along with an armory of useful skills that will help you unravel whichever programming language you decide to learn first. We’ll only be covering the major key points that apply to all programming languages, so
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we’ll be shying away from topics such as object-oriented coding and command line navigation, as those are things which are language-specific. Additionally, there will be no software required for you to download in order to follow along with this tutorial as we won’t be writing any code to keep things simple and concentrated. This video is meant for those who are interested in computer science and programming but have no idea where to start and have little to no background information on coding, and so if that sounds like you, then strap Sean and I work our way through the wacky world of computer science, starting with the biggest question probably on your mind, which is what even is programming? Well, the dictionary defines it as the process of preparing an instructional program for a device, but that’s a really confusing definition, so in layman’s terms what exactly does that mean? Essentially, it is attempting to get a computer to complete a specific task without making mistakes. Imagine this, for example: you want your less-than-intelligent friend to build a lego set, except he has
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lost the instructions and can only build based on your command. Remember though, your friend is far from competent, and so If they are not given very specific instructions on how to build the set, there are many mistakes he could make. If he thinks like a computer, then if there is even one piece that you have not told him specifically where to place and how to place it, the entire lego set will be ruined and he will be left to suffer a complete mental breakdown causing the whole goal of the project to be corrupted. Giving instructions to your friend is very similar to how programmers code. Instead of a less-than-intelligent friend, you have a less-than-intelligent computer, and instead of instructions on how to build a lego set, we are feeding it information on how to complete a program like a game or web application. An important thing to note is that comptuers are actually very dumb. We build them up to be this super sophisticated piece of technology, when in actuality, a computer’s main functionality comes from how we manipulate it to serve our needs.
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Now, programming isn’t as simple as giving your friend instructions since in a programmers case, the computer doesn’t speak the same language as you, the computer only understands machine code, which is a numerical language known as binary that is designed so that the computer can quickly read it and carry out its instructions. Every instruction fed to the computer is converted into a string of 1’s and 0’s and then interpreted by the computer to carry out a task. Going back to the lego example, this process would be like if he was not only less-than-intelligent, but to make matters worse, he could not understand english and only speaks in mandarin chinese. In order to speak with him, you have to convert the instructions that you understand in english into the language that your friend understands. This process is essentially what you must do for your computer in order to make it understand the instructions you give it. The big difference between the two examples, however, is that it is very difficult for people to understand machine code and binary. Directly translating what you want the computer
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to do into machine code is extremely difficult, in fact almost impossible, and would take a very long time to do if you could. Each program is composed of millions upon millions of those 1’s and 0’s, so how, exactly, are we supposed to translate our instructions into machine code? This is where programming languages come into play. Programming languages are fundamentally a middle man for translating a program into machine code. These languages are much easier for humans to learn than machine code, and are thus very useful for programmers. Going back to our lego example, a programming language would be sort of like an interpreter, that’s able to take the instructions you give them in english, and translate them into instructions your non-english speaking friend can understand. This makes programming languages extremely useful and the backbone of almost any good program. Think of programming languages as not english, and not machine code, but somewhere in the middle. There are many different programming languages out there that each have their own unique
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uses. Languages such as Python and Java act as general purpose languages that can perform a variety of computational tasks, while RobotC or HTML/CSS are languages designed for more specific purposes such as moving a robot or constructing a website. Languages can also vary in how powerful they are. For instance, JavaScript is a scripting language that is designed for smaller tasks while java or python can carry out much more computationally taxing processes. We measure a programming language’s power, or level, by how similar it is to machine code, the series of 0’s and 1’s we talked about earlier. Low-level programming languages such as assembly or C are closer to binary than a high-level programming language such as Java or python. The basic idea is that the lower the level of your programming language, the more your code will resemble what the machine can interpret as instructions. Aside from the different purposes that each language fulfills, choosing a programming language typically comes down
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to a matter of preference, as there are usually many languages that accomplish similar tasks. Try different languages, and decide which one’s rules, interface, and level of simplification you like best. So now that we know what programming is, how do we actually write code? It’s not like we can simply type words into a text document and automatically assume that the computer can translate it into machine code, read it, and carry out a task like opening up a browser. And additionally, we can’t just write down rubbish in certain programming languages mentioned in the previous episode and expect the computer to understand. So how are we supposed to write code then? Well, the answer is with an IDE. An IDE, which stands for Integrated Development Environment, allows the facilitation of code by a computer. IDE’s provide a graphic interface on your computer in which the programmer can easily write, run, and debug code without having to worry about problems with compilation or interpretation of the program. Think of an IDE as any other program on your computer such as a game, a browser, or even the file explorer, except we’ll be using it to write code. IDE’s are able to turn your code into
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machine code and run it through the computer to produce results. In addition to providing a place for programmers to develop their code, IDE’s provide some extremely useful tools for programmers to ease the job of writing code, such as built-in error checking because as we’ll talk about later; code doesn’t always run correctly, auto-fill in for frequently used words or phrases, and project hierarchy which will help you organize and manipulate the files within your project. Back in the olden-days, before IDE’s, code used to be written on punch cards and then fed into computers which would take hours and cause a lot of pain. IDE’s nowadays act as a sort of fast-track to writing code and make things a whole lot easier for programmers. An example of a specific IDE can be seen on your screen now. In the center you can see the program that is currently being written, and right below it the console, which can print out useful information for the programmer. This specific IDE is used to write java code. IDE’s are extremely powerful and will be used in almost 100% of your programming projects. So through these IDE’s we are finally able to write and compile code smoothly without
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worrying about the computer not being able to understand it. The next problem we run into then becomes how do we write this code in the IDE, because it’s not like we can just type random words from a certain programming language and expect the compiler to understand it. This is where a programming language’s syntax comes into play. Now, just as if you were learning a real language, learning a computer language can be very similar. Some have different styles that may seem odd, some may make you use abstract or weird concepts which may be confusing, and like all languages, programming languages have a set of rules that you must follow when writing code in that language, and at the forefront of those rules is grammar. Programming grammar is referred to as syntax and is very similar to real-world grammar. Each programming language has its own syntax, or rules, that you have to follow to a tee if you want your program to run correctly, just as if you were speaking in real life. These can be things such as how you type out certain functions, what you put at the end of a line of code, and how you set up certain functions. Each language is unique in its
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syntax, and while some may share similar rules, all will have some quirk which makes it stand out from the rest. Syntax is something that catches a lot of people off guard, since many expect every programming language to follow the same set of rules, but as we spoke about in the last segment, because each language is specialized for a specific task, each needs its own set of rules to function. Breaking or disregarding these rules will result in an error, just how breaking or disregarding rules in real life will result in an unintended message. As an example. If we wanted to do something simple such as initialize a variable, which is something we haven’t covered yet but the example is still relevant. In java, you’ll notice we have to specify what type of variable we are defining in this case an integer, and also add a semi-colon after the statement. In python, we don’t even need to define that we are trying to create a variable and just have to type what we want to create, and in javascript, we just specify we are making a variable, but do not include what type of variable we want to make. Even in this simple example you can see how much syntax
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matters when learning a new language since while the goal of our program remained the same, define an integer with value three, all the programming language shown took different approaches. All these languages require that you follow this syntax because remember, computers are extremely dumb, if you forget one semicolon or misplace a character, the entire program will not run and send you back a syntax error, which is something we will talk about later. Think of this as if you forget a comma in a sentence and the entire context of what you are trying to say get misinterpreted. For example, in the sentence “let’s eat, grandma”. If you were to forget that comma, while it may seem like a small mistake, it changes the entire context of the sentence, making it sound like you’re about to eat your grandma. The same rules follow for programming, if you forget a semicolon, the entire context of your program could be corrupted and misinterpreted. Now another thing which makes IDE’s so useful is that they will let you know if and when there are syntax errors in your code. Syntax errors of course being parts of your code which do not follow the rules we talked about previously. The IDE will tell you where in
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your code the error is, and also won’t let you run your program until the error has been fixed. Because of how important syntax is to writing code and learning a new language, it's recommended that you learn the rules and syntax of a language before beginning to write complex programs in that language. Most of the rules are tedious to learn but easy to master and as soon as you can do that, you’ll be able to easily identify syntax errors and take care of them easily. That covers the basic gist of syntax and programming rules, so now that we know HOW to write code, and WHERE to write code, we next need to cover what happens after we have typed out our program and run our code. Because writing a piece of code for a game or for a database is cool and all, but after the computer interprets the program, how will we know what’s happening, and whether it is working or not? Well, programmers do this by looking at the console. The console is a text interface within the computer that us programmers can use for a variety of different purposes. If you remember, a short while ago we showed a picture of a basic IDE, and one of the main parts of that picture was the console. The main use of the console is to output text from the program. This is usually done using
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a print statement. A print statement is a command that does exactly what it sounds like: it prints text to the console. This print statement is the first piece of ACTUAL CODE we’ve talked about in this series, and it’s about as simple as it gets. The print statement, despite its simplicity, is one of the most important functions in programming and exists in some form in just about every programming language. The most basic thing you can ask the print statement to do is just simply make it say something. This is done by instructing the console to print, and then include whatever you want to be printed inside the parentheses. For example, in python, the segment of code print(“Hello World”) will cause a message reading “hello world” to appear onto the console. Pretty neat. The print statement is also vital for viewing and interpreting the computer’s output from a program. For instance, if you tell a computer to run a simple calculation, for instance to determine what 4+3 is, it will run the program internally and compute an answer. However, what is the purpose of having the computer run this program if you will not be able to tell what the result is? Instead of simply telling the computer to perform this calculation, instruct the computer to print the output of the program to the console,
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and upon the program’s completion, 7 will appear on the console. As you can see, the console allows us to easily print information out to the developer for a variety of uses. It is important to note that the print statement varies depending on the programming language being used. For example, in Java there are multiple versions of the print statement depending upon whether you would like a line break after the printed text, and specialized print statements which make your code more efficient. Also, the general syntax of using a print statement and certain nuances of its function can change between languages. However, you can generally rely on it carrying out the same overall function, as it is a foundational statement for programming in general. So print statements, they print information out to the console for the developer to use, nice. All of its functionality makes the print statement, along with the console, a very useful developer tool. However, it is important to remember that that is all it is: a developer tool. The console is not really meant to be viewed by the end user of your program. It tends to be hidden away behind the scenes, and other methods of displaying information such as displaying text, graphics, or images are used to convey information to the user instead. Think of it like this, when you’re using your phone, you see the console in none of
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the programs you use. So while you can use the console to give yourself information about how your program is performing, don’t try to implement it in the final product because it fundamentally just isn’t meant for that. Overall, remember to use the console to its fullest extent when writing and fixing problems in your programs, as it is a great tool to use to tell how your program is performing behind the scenes. So now that we know a whole bunch of information about programming languages and how and where to write them, along with the print statement under our belts, let’s go over some intuitive things the computer can do all by itself, without you having to tell it how to. More specifically, we’ll be covering basic number mathematics as well as string math Starting off with basic mathematics, the computer already knows how to do simple arithmetic. This includes addition, subtraction, multiplication, and division, all of which are represented by the symbols shown on the screen now. In any IDE that you may install, you’ll be able to print out the answer to simple math problems using the print statement, which may seem counter-intuitive because why would you use the computer to do math when you have a perfectly good calculator on your phone, but you have to remember that computers are
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dumb, and anything we want a computer to do we have to build up from scratch. Basic arithmetic, while simple, helps out in almost any program you may write. For example, if we wanted to build a basic calculator app, we’d need to utilize this functionality in order to correctly display the answer to an arithmetic problem when our user tries to add, subtract, multiply, or divide two numbers. Now in addition to the 4 basic math equations, most programming languages include an additional operator known as modulus. If this is your first time hearing this word, don’t worry, since it's not usually taught in math classes. Modulus allows us to get the remainder of a divisional operation. For example, when we take 10 modulus 3, we are essentially telling the computer to take 10, divide it by 3, ignore the actual answer and just give us the remainder of that operation in this case 1, since when we divide 10 by 3, the answer is 3 remainder 1. The 1 in this case is what gets printed out to the console. If there is no remainder,
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say in the case that we take 50 modulus 2, since the remainder is 0, the function would return 0 if we were to print it out. This can be extremely useful in many cases, the most obvious being if we want to determine whether or not a certain integer is even or odd. If we take a certain number modulus 2 and it returns 0, then we know it's even since any even number divided by 2 will always result in a full answer without a remainder, but if the system returns 1, then we know that the integer is odd. You will find yourself using the basic math operators a lot more than you think, so it's good to keep them in mind when writing your programs. Now our computer can work with numbers, as well as Strings. Strings by the way are another way to just say text. For example, “hello world” is a string, The letter “a” is a string, anything enclosed by quotation marks is denoted as a String in programming language. We’ll cover more about Strings in a bit when we talk about variables, but for now let’s continue. We already talked about printing strings to the console, but let’s
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say we’re making a game, and we wanted to print out the statement” “Game over, 4 was your final score”. Now while we could just make a string that says that exact phrase and print it out to the console, in some cases it would be more useful to print out the actual integer value, especially in the case of a game where the score can change each time you play, because score definitely isn’t always going to be 4. Well, we’re also able to print multiple strings of text, and even integers by “adding” them together in the print statement. This is called concatenation. Continuing with our score example. If we wanted to print out the statement “Game over, 4 was your final score”, using 4 as an integer rather than a string, we could do this by breaking down the statement into two strings and an integer like so. Print (“Game over, “ + 4 + “ was your final score) We of course begin with a print statement, which again will be different across all languages. Inside the print statement we start off by printing the string “Game over, “. Now
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here comes the important part, from there, we use a plus sign and add 4 to the print statement, just like if you were adding two numbers. Then, we can repeat this process with another + sign for the final string “ was your final score” and we’re able to print out the entirety of our statement easily. Doing this, we can easily print out multiple different strings and integers together in one print statement. We could also combine the two lessons we’ve learned thus far and do something like “Game over, “ + (4+4) + “ was your final score”, in the case lets say where we have a game which gives you a base score, then 4 points for a certain task you completed. This demonstration also displays another important part of programming, which is that oftentimes to get your program to be the most efficient, you have to combine aspects of code. Now it's important to note that the computer will take whatever you put in parenthesis and print it out character for character, so oftentimes programmers will forget to add a space onto the end of their strings. This can result in an small mistake in which the
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string from the previous example will be printed out as if to say “Game over,4was your final score” which isn’t that appeasing when displayed on screen to the user, so it's good practice to always put a space after and before your strings to make sure this doesn’t happen, and your string doesn’t end up like this. Another important thing to note is the difference between “4” in quotation marks and 4 without quotation marks. Now “4” in quotation marks is treated as a string rather than a 4 without quotation marks which is treated as a number. This may not seem like a big deal, but again computers are dumb, and if you try to do math with a number in quotation marks it will return an error, because the computer doesn’t understand that you’re trying to preform the operation on a number, and it thinks you’re trying to add an integer to a string, which is a big no-no in programming. So when you are programming make sure to make a mental note of whether or not you want to make something an integer, or a string, because that type of stuff makes a big difference. Alright, that concludes our segment on the
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base power of computers. Now next up we’re going to be covering one of the most important components of computer science, so make SURE you pay attention because next up we are going to be covering variables, what they are, and how we use them. First of all, what exactly is a variable? A variable is simply something that can store information and can be referenced and manipulated. Think of variables like a cardboard box. Cardboard boxes serve as a means to store items in them which can be changed out, replaced, and modified. Variables are like cardboard boxes that store information for the programmer to reference, manipulate, and refer to. Each variable simply has a type, a name, and a piece of information stored inside of it. The type and piece of information will be covered next and the name is simply a name for the variable, think of it as writing out a label on the cardboard box in sharpie. Now, there are many different types of variables that a programmer can use, but right now we will just be covering what are called “primitive variables”, which include integers, booleans, floats and doubles, strings, and chars. We’ll start off talking about an Integer. An integer, or int for short, is as simple
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as it sounds: a variable that can store an integer value. This includes all whole numbers from -2,147,483,648 to 2,147,483,648. Now notice how I said whole numbers, integer variables CAN not and WILL not hold any decimal values, so keep that in mind when using variables. Secondly is a boolean. A boolean is a very primitive variable which can store a value of either true or false. Boolean variables can ONLY hold these two values, and are extremely useful for conditional statements, which we will cover soon. The next two types of variables are floats and doubles. Both of these variable types are floating point data types, which essentially means that these variables can store numbers with decimal places. Whereas integer values cannot hold decimal values, floats and doubles can. The main difference between the two is that a float variable can store numbers of a precision up to 32 bit, while double can store numbers with precision up to 64-bit. Essentially, a double can store more decimal places than a float, so it all comes down
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to how precise you want the variable to be. Up next we have string variables, which are like the strings we’ve actually talked about beforehand except stored somewhere in a value. String variables can store strings of letters, which are just words and sentences. Strings are useful for displaying text and storing input information. Strings can also be concatenated together to form combinations of string variables and prewritten strings. This is very useful for outputting information in a readable format for the user. For example, imagine that we have a string called “name”. The code asks for input, and stores that string of text in name. To output this information to the user, rather than simply displaying their name, you can add the phrase “Your name is:” and make it into a sentence by concatenating “Your name is:” + name + “.” This makes it easier to read your code, while also adding variability to your code, which always makes things more interesting for the end user. Finally, we have char variables. Char stands for character, and just as the name suggests, they can each hold one character. This is useful when a programmer wants to read one button press or one character in a string without using a string variable. A specific
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example is making a game that is controlled by the keyboard. The program needs to recognize the character that is pressed, and translate that into carrying out some function. Now strings can also hold one character, but char’s can’t hold more than one character so keep that in mind when defining variables. Now, why are variables so useful? Well, being able to store information in a format that can be easily referenced later is essential for any good program. Oftentimes in code you’re going to want to keep track of things such as a user’s name or score, and so by creating a variable called “name” or “score” you can store this information in that variable and then reference it, add to it, or modify it. Also, many times, the program will have to take input from the user, which cannot be pre programmed into the code, and thus a variable is required to store the information. A program may also rely on factors that will change as the program progresses, in which case a variable is once again required. Also, taking these variables and manipulating them is quite necessary for carrying out many of the tasks you want a program to carry out, for instance multiplying int variables or concatenating string variables. Overall variables are the backbone of any good program and you’ll
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find yourself using them often if you want clean and efficient code, so it's best that you learn what types of variables you need to use and when. So now that we know all about the different variable types and we’ve talked about them a little bit, now we’re going to delve further into what happens when we actually define, or create, a variable, how we reference them, and how we can manipulate them for our programs. To start, let's go over what happens when we define a variable. Now when we write a line of code which initializes a variable, and that code is executed, the computer essentially creates a little space in memory that stores your variable name and its contents so that it can be referenced later. Going back to our cardboard box example. Think of this as if you have a storage facility, and you make a new cardboard box, labeled “Name” and inside of it you put a piece of paper with the word “NullPointerException” on it. Now, anytime you want to know the contents of your name box, you could simply look inside and see that it has the contents “NullPointerException”. This is what the computer does, except the
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storage facility is memory, the box is a variable, and the contents of the box are whatever the variable is set to be equal to. Any time you want to know the contents of the name variable, you can simply call it and the computer will pull the information that is stored in that variable out and use it how the user sees fit. Another thing to note really quickly is that you can actually make a variable without putting information inside of it. This would be like if you built up a new cardboard box, gave it a label with a sharpie, but just didn’t put information inside of it. You’re simply saving that space in your warehouse for later. This can be because you want to store information in it later down the road, or if you’re going to use it to store information given to you by the user, in which case you CAN’T give it information since you don’t know what the user will input. Just note that if you try to reference, or point, to a variable which does not have any information in it, you’ll get what’s known as a NullPointerException, which despite being an awesome name for a YouTube channel, is something you generally
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want to avoid when programming. Now, programming languages allow us to do some pretty cool things with these “boxes” that we’ve created. For example, let’s say we created a second variable “channelName” and instead of setting it equal to “NullPointerException”, we instead set it equal to our already created “Name” variable. This doesn’t create a space in memory for this new variable; however, it simply points to the same location of memory we have already created for the “Name” variable. Going back to our storage facility example, this would like if instead of creating a whole new box labeled “channelName” and storing a sheet of paper with the word “NullPointerException” on it, we instead simply added another label below the “Name” box, entitled “channelName”. Now, we have two variables but both point towards the same contents, that being the string “NullPointerException”. We usually do this to save space in our code for things that we know are going to have the same value. Variables can also be updated throughout your code. For example, let's say you had an “Age”
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variable, and inside it was the integer 17. Then you celebrated a birthday and wanted to update your age. All you have to do is reference the variable, and set it equal to whatever new integer you want the variable to hold, in this case 18. This would be the same as having a box labeled age, with a sheet of paper reading 17 inside of it, and then taking that piece of paper out, erasing 17, replacing it with 18, and then placing it back into the box. Doing this, we are able to easily update the contents of our variables throughout the code as things dynamically shift. As another example, if you were making an RPG, your character will likely have stats such as attack, defense, mana, etc. As the game progressed you could continuously update the variables so that the player could get more powerful the further along that they went through the game, and you wouldn’t have to create new variables. You would just simply need to keep grabbing that box from your storage facility, erasing and replacing the numbers on the piece of paper, and then continue along with your code. Just keep in mind that these variables are nothing more
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than places in memory in which a certain value is stored, so we can easily update the numbers, and their place will remain constant. After a code has run its course, the place in memory is deleted until you run the code again and the program dedicates space for the variable again. Each time you run the code, you're making new boxes in your storage facility, and at the end of your code, you destroy them all to make room for new boxes next time. Another cool thing you can do with variables is add them, subtract them, multiply them, divide them, and even modulus them. Now this mostly only works for integer variables as multiplying and dividing strings doesn’t make too much sense. But if you were making a calculator app and you stored the first number the user entered as num1, and the second as num2. You could then multiply num1 and num2 together, and either print them, or store them in a new variable entitled result. Then, each time you run the program, the user could input new numbers into the num1 and num2 variables, and they would simply be set to those new integers and return the result that corresponds to those specific numbers. This allows for
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you to keep easy track of which numbers are which and what’s going on in your program which is extremely useful. Also, while you cannot subtract, multiply, divide, or take the modulus of strings, you are able to add them. Let’s say you had a string Str1 with the contents “Hello “ and a Str2 with the contents “there”. You could add Str1 and Str2 to create a string that had the contents “Hello there”, either storing it in a third variable or printing it out to the console. The last topic we’ll be covering on the topic of variables is the naming conventions of a variable, which albeit may seem odd, but it's extremely important when trying to read your code so we will be covering it now. Now, variables have to be one continuous string, and so if you wanted to make a variable that stored the player score, you’d have to find some way to combine the words player and score, since you can’t have the phrase “player score” be the name of a variable. All programmers have their own personal preference when it comes to naming variables, but the one we will be using on this lecture is called CamelCase,
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which is the process of not capitalizing the first word, but capitalizing every word that follows it. Going back to the player score example, using the camelCase method, the variable would be called playerScore. This allows us to easily identify each word and becomes really useful for long variable names like thePlayersScoreBeforeFinalBoss”, whereas if we just type it out without capitalization, it would be really confusing. This will help a ton when you start to find bugs in your code and need to quickly scan your program to figure out whats wrong, and adds to the overall readability of the program. Other programmers might use different naming conventions like using underscores to separate the words in a phrase, but for now we’ll be sticking with camelCase. Next, we’ll be moving on to conditional statements, which at their core, are statements that change the path of our code depending on certain conditions. For the sake of keeping things simple, for this section, red lines will connote that our code will NOT be following
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that specific path, and green lines will mean that our code IS following that path. The main type of conditional statement that programmers use is the if statement, and this will show up countless amounts of times in any program you write. It is as simple as it sounds: if some condition is true, and usually the condition will be enclosed by braces, then carry out the instructions located within the if statement’s brackets. Else, do another thing. Now, brackets are used in most programming languages to indicate a segment of code which will run. It works like this, if the condition in parentheses is true, then all of the code contained within the brackets will run, and if the condition in the parenthesis is NOT true, then it will skip over all of the statements within the brackets. A quick note is that while this is the case with most programming languages, some; like Python, use colons and white space to determine where a piece of code starts and ends, but for the sake of this series, we’ll be using curly braces. Now, the condition within the parenthesis can take on thousands of different forms such
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as if the value the string variable Name is equal to “Steven” or if the player's score, stored in an int variable, is greater than 5, the list goes on and on. Each of these statements is evaluated as a boolean, which you will remember from when we talked about variables is either true or false. If the boolean is true, we run the code inside the curly braces, if it’s not, we pretend everything inside the curly braces never existed and move on with our code. The if statement comes with two more additional statements that can go with it: else if and else. Else if is a conditional statement used directly after an if statement, and carries out mainly the same function as an if statement. However, the else if statement will only be evaluated if the preceding if (or else if) statement is bypassed due to its condition being false. So we would run through it like so, if something is true, we would run the code inside of that statement’s curly braces. Else, if that something is not true, BUT another
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statement inside of parentheses is true, we would then run THAT code segment. And if neither of them are true, we would skip both segments of code and move on in our program. This is a hard concept to wrap heads around so let’s do an example. If we had a program that evaluated the if statement if (age = 10), we could then have a statement under that which stated else if (age = 12). Now, if the age variable was 10, which we can see from the example it is, then the code immediately following that conditional statement in the brackets would run. The else if statement we made would not even be tested since we know it is going to be false, and thus the print statement inside of THAT conditional statement’s brackets will be ignored, and the code will move on to the rest of the program. Now, for example, let’s say we changed the age variable to be 12 instead of 10. Now, instead of the first conditional statement being, true, it actually evaluates as false, since age no longer equals 10. So what we do now, is first skip over the print statement which prints out that the age is 10, since it’s not. And now we evaluate the else if statement. We check if age is equal to 12, which again it does, and so now we run all
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the code inside of that conditional statement before finally moving on to the rest of the program. So as a review, we check the initial if statement, if it’s good we run all code within that if statement’s curly brackets and move on with our program, if the initial if statement is NOT true, we then move on to any else if statement’s and evaluate if THOSE conditional statements are true. We can have as many else if statements as we want, although this could lead to clutter amongst your code so we’ll talk about some alternatives later on to help this out. Now that takes care of the if-else statement, so now we’ll move on to the else statement. The else statement once again comes after an if or an else if statement, and will carry out its instructions no matter what, as long as the preceding statement/statements are evaluated as false. If we went back to our previous program, we could add an else statement which would only have the code in its brackets run if the age variable wasn’t “10” or “12”. This would catch all cases of the program that didn’t fit our parameters. It’s good practice to ALWAYS have an else statement at the end of your conditional statements to catch any weird cases that may come up in your program. Now remember back to the fact that we can have thousands of else if statements, after
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a while that can get pretty cluttered, and so another very useful conditional statement which helps circumnavigate this problem is the switch statement. A switch statement is functionally similar to many if and else if statements together. You write a switch statement in the form of switch (variable), and then below that you write how many cases that the variable could be. For instance, if we wrote switch(var), then under it we could write out 5 cases that the variable var could be, and then the instructions listed under that case to be carried out if the var variable is equal to that case. Now switch statements are different since instead of using brackets, they use a colon to signify the start of a set of instructions, and a break statement to end it. This is very useful because you are able to essentially use many if and else if statements without having to write nearly as much. In switch statements, you just always have to remember to include a default case at the bottom of the expression to denote any and all cases that don’t meet the above requirements. This simply catches all of the inputs that don’t fit within the programs main cases. It’s very similar to an else case at the end of an if-else chain. Now, why are these statements so useful? Well, many times, programmers want their programs to function differently depending on different conditions. For instance, a program could
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function differently depending on the information that the user inputs, such as allowing a user to use a program or not use a program if they are above or below 18 years old respectively. Or in say a video game, if a user’s experience level is above a certain threshold we might want to give them harder opponents to battle. Another example could be a program which changes the color scheme depending on the time of day. Or even more simply, if a user presses a button that is meant to move on to another screen in an app, the programmer would only want the app to change screens if the user clicks that button. A program without conditional statements would do the same thing every time, and would be very primitive compared to one that can change depending on its conditions. So now that we know how to make and use variables, how to compare them, and what we can do with those comparisons, let’s move on to another foundational concept of computer science: arrays. Now we’ve already talked about variables, and how great they are for storing singular bits information for making our code more simplistic, but one of the biggest drawbacks that come with variables is their inability to hold more than one piece of differing information. For example, let’s say you’re making an app which allows users to create a grocery
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list. Well there’s no real easy way to create lists using variables, because it's not like you can have one variable store the names of 7 or 8 different food items. Remember, we can only put one piece of paper in our cardboard box; no more. And besides, even if you were to add multiple items to one string variable, you still would have a lot of trouble doing simple tasks you might want from a list like searching through it or splitting it or even deleting items from the list when you’re done with them. This is the problem that using arrays solves for us. An array is, as you may have guessed by now, a list. You can have an array of integers, an array of strings, and even an array of other arrays which is something we’ll cover in a minute. Programmers use arrays when they want to store a lot of variables containing information that is all related to each other, such as a grocery list or a high score list in a game. Think of arrays as a column in excel or google sheets. You have the title at the top and then below it are a bunch of bits of information which all relate to the title. Arrays are super useful when programmers want to store a lot of information that can
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be easily searched through because programmers have developed methods of breaking down and using arrays to find specific information in arrays full of thousands of different variables. As an example to show just how useful arrays are, let's say you’re a startup company that owns an app that has 100,000 users. Every time a user wants to create a new account, they input the username they want and then your program will have to check to make sure the account name hasn’t already been taken. Doing this requires you to search through the information of all 100,000 of your users to see if that username has an account with your service. An array would be able to contain all of this information and make it easy to search through and find out if the account name has been taken with little to no delay. Now the single most important thing to note about arrays is how you reference each element of the array within them. Let’s create a basic array called numbers, and inside of it put the digits 1-10. Now when we want to refer to each cell in this array, we call upon its “index”. An index is just a fancy way of saying that numbers are placed within the array. Now you would think that the first integer in this array would be the first index,
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the second would be the second index and so on, but that’s not the case. In computer science, programming languages refer to the first cell as the 0th element in the array. This means that if we were talking about our array of numbers we just made, the number 4 would actually be in the 3rd index, 5 would be in the 4th and so on, so instead of starting our count from 1, we start from 0. It’s extremely weird and confusing but it's one of those programming quirks you are going to have to memorize and commit to memory. If you were to not follow this nomenclature and you refer to the last element in this array as the 10th, you get what is referred to as an “out of bounds” error, since you are trying to reference the 10th element, but there is no 10th element. What you’re actually trying to do is reference the 9th. Another extremely important thing to note about arrays has to do with their size. When you initialize an array, you can do it either one of two ways. You can either populate it with the elements that you want contained in the array right then and there, creating and filling the array at the same time, or you can define how many elements you want
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in the array-essentially the arrays size- and then populate it with elements later. This is because when we initialize an array, it creates a space in memory that has a size of exactly what you give it, no more no less. This is great for when we want to access elements in the array because we can do so instantaneously, but the one downside is that we can’t increase the size of the array later on, all array sizes are final. Think of it like setting up a bookshelf with books. By populating a bookshelf with a certain number of books and then moving on and filling the next shelf with different books. We have no way to go BACK and add books to that first shelf without shifting everything. Once we decide how much space to dedicate space for an array in this case, there’s no way to ADD more space. Once again because this is extremely important to remember, this means that once an array has been defined, there is NO WAY to change the size of it. If you have an array titled
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“Names” with a size of 8, and you try to add another name to the array you will receive an error, so be careful when messing around with array sizes. Of course, you can always go back at the start of the code when you initially MAKE the array and allocate more space to it if you find out you need more space to hold items, but once it’s defined, you CANNOT change its size. Another small thing I want to touch upon really quickly is that when you initialize an array, you must determine which type of array it is right then and there. For example you have to specifically say it will be an array of strings or integers when defining it, and also you’re not allowed to mix and match, meaning you can’t have an array full of integers with a few strings and some doubles thrown into the mix. They have to be all the same type. Now the last thing we’re going to cover on arrays is a little funky, and that is the practice of putting arrays inside of arrays. If you make an array of arrays it's referred to as a 2D, or 2 dimensional array. Think of these as matrices if any of you have taken
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algebra classes. Now If you haven’t, think back to our google sheets example but instead of just columns, we would add rows as well. So now, each element in our array wouldn’t simply be just a String variable or an Integer variable, but an entirely new array with its own set of values and elements. The way we index these is mostly the same, except we would have 2 numbers to index instead of 1. We start with the row and then the column. So a number in the position (0,2) would be in the first row three columns down, in this case the name Clint. A number in the position (1,1) would be two rows down and 2 columns across, in this case the name Chris. You get the idea. Now you can also make 3-dimensional arrays by putting an array inside an array inside an array, but that's a little above what we’re going to be covering so I’m gonna cut it off there. Next up we’re going to be talking about loops, so what exactly are loops? Next up we’re going to be talking about loops, so what exactly are loops? Next up we’re going to be talking about loops, so what exactly are loops?
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Next up we’re going to be talking about loops, so what exactly are loops? Next up we’re going to be talking about loops, so what exactly are loops? Well as you could probably tell by that statement right there, a programming loop is a statement that is used to run certain instructions repeatedly, just like how the opening statement of this topic was repeated 5 times. Loops are very useful for a variety of reasons. For instance, imagine you want to print something 15 times. Sure, you could just copy and paste the print statement 15 times. But this is really annoying to have to do, and becomes even more unrealistic when that number goes up to, say, 100 or so. Now what if instead of rewriting the same instructions over and over again, you could simply place the print statement inside of a loop, and it will occur as many times as you would like, that’s the power of loops baby. With loops we’re able to repeat parts of code multiple times. Now there are three different types of loops that we will be discussing today. And up first is the for loop. A for loop is very useful for situations described above, where you would like to carry out a certain set of instructions numerous times. The syntax for a for loop varies depending on the language, however it usually consists of three parts. An integer value, a condition
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which the integer value must meet in order to exit the loop, and an operation to modify the integer value after the instructions inside of the loop are completed. Each time the for loop runs, the operation you set will be performed on the integer, and as long as that integer still meets the condition you set, usually being greater than or less than a constant value, the for loop will continue to run. Eventually, when the integer has been modified by either increasing or decreasing it to the point where it no longer meets the condition, the for loop will terminate and the code will continue to run. For example, let’s say our integer value was i and we set it equal to 0, then we set the conditional statement as i being less than 3, so basically we’re saying that as long as i - the variable we just created - is less than 3, continue running the instructions contained within the loop. Finally, we make the operation i + +, meaning each time the loop runs we will increase it by one, and inside the loop let’s just put a simple print statement. Now let’s run through the loop. We start with i = 0, 0 is less then 3 so we enter the loop and print out Hello World. Now that the instructions are done we add 1 to i making it 1. Moving on, 1 in less than 3 again, so we once again enter the loop and print out
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Hello World. Again, we add 1 to i, making it 2 now. 2 is still less than 3 so we enter the loop again and print out hello world. Finally, we add 1 to i once again and it becomes three. 3 is not less than 3 though, it is equal to 3, and so we don’t enter the loop and it terminates, moving on to the next segment of code. This is a simple example, but you can extrapolate it across programming to fit your needs. Now when using a for loop you have to make sure to set up a condition that, given the initial integer value and the operation, will at some point not be met, to avoid creating an infinite loop and crashing your program. An infinite loop occurs when you give a for loop a condition which will always be met given the parameters of the program, and so the software crashes. For example, a for loop beginning at 10 and checking if i is ever less than 0, and then adding 1 to i at the end of the loop will never terminate, since i will just increase infinitely. After the for loop is the very similar for each loop. A for each loop (or a for-in-list loop, in python) is used for iterating through arrays or lists. Essentially the loop will go through each element in the array and carry out some set of instructions for each value.
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If you would like to read all of the elements in an array and compare them to some value, or perform some operation on them, a for each loop is extremely useful. So for example, we could have a for each loop which iterated across an array and simply printed out the value of each array location. Next up, we have the while loop. A while loop will continually carry out its instructions while a conditional statement given to it is true. This can be as long as a certain variable is true, as long as a number is less than another number, or while a value is still equal to another value. While loops are different than for loops in that the loop is not contained within one statement, but stretched out and will continue to run so long as its condition is true. Like a for loop, you can make the condition such that it will eventually return false and exit the loop, however while loops will not crash your computer should you create an infinite loop. In fact, it is very common for while loops to run infinitely, as, for certain programs, you would like the program to continually be iterated through instead of running once, all the way through until you exit out of the program. When programming a game, for instance, a while loop would be used to iterate through your
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code, continually refreshing the screen as the game runs. From there you could perform operations on the screen to make the game playable. Creating an infinite while loop would simply be done using the syntax while(true), as the condition true will always be evaluated as true. Finally, I’d quickly like to cover an extension of the while loop, the do-while loop. Do-while loops are very similar to while loops, except they will carry out their instructions at least once, even if the condition is false, and then will carry on like a basic while loop. Essentially, the conditions inside the loop will run AT LEAST once, and then if the condition is still met they will run again and function as a normal while loop. As you can see, loops and their many varieties have some extremely useful functions. Using them, you are able to perform an operation many times in a row, you can iterate through arrays and lists, and overall decrease the clutter of your code. Next up, we’re going to take a break from learning about common programming statements, and dive into what happens when the code we write doesn’t work. More specifically, we’ll be covering the different types of errors that can occur when you’re programming, and what causes them.
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Now when you’re writing code, you have to understand that things aren’t always going to go the way you expected them, and sometimes the program doesn’t always work as you had intended it to. We programmers call these errors and while annoying, they are always going to come up in computer science and so it's best to learn what they are and how to deal with them. Often referred to as “bugs”, errors in scripting languages can be narrowed down to one of three “types”: syntax, runtime, and logic, all three of which we will be covering in today’s video. To kick things off, let’s talk about syntax errors. These are usually the easiest of the 3 to solve since they are oftentimes something that can be fixed within seconds. If you remember back to earlier in the video when we talked about syntax and programming rules, we said that if you were to break the programming rules, or syntax, that it would result in an error. Well that’s what syntax errors are, parts in your program where you fail to meet the programming rules and so the computer doesn’t know how to interpret your code. This can be anything, from forgetting a semicolon at the end of a statement in java, accidentally
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defining a variable with two words instead of one, or even just misspelling the word String when you’re trying to define a string variable. Lucky for you guys, these errors are extremely easy to fix since you just need to figure out where the error occurred and what the syntax rule you broke was. Now thinking back to IDE’s, we mentioned that IDE’s are so useful because they do precisely that, they underline syntax errors and usually provide helpful hints as to how to fix them. Think of syntax errors as small misspellings or grammatical errors in an essay you’re writing, annoying; yes, but not the most infuriating things. Another useful thing about IDE’s when it comes to syntax errors is that the program will actually restrict you from running the code unless all syntax errors are cleared, making them even easier to identify and fix. The second type of error we will be covering is the runtime error. These errors don’t show until you actually “run” the code, hence the name “runtime” error. Runtime errors are caused by a statement in your code that SEEMS seems logically sound, but the
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computer physically has no way of computing it in a reasonable amount of time. The most common of these errors is one which we’ve already talked about; the infinite loop. As a refresher/example, think of an infinite loop like this. Say you sat your friend down in front of the TV, put on the Office on repeat, and told him he could leave as soon as Michael made a “That’s what she said” joke. Seems pretty simple right? WRONG, because instead of putting in the Office, you put in FRIENDS on blu ray. No michael, no inappropriate joke, meaning your friend would be sitting there for the rest of his life probably confused as to why Dunder Mifflin looks so much like a coffee shop. This is essentially what happens with the computer, you give it some condition that it has to complete before the program can terminate; however, you give it no feasible way to finish that task. This puts the computer in error mode and most likely will crash your program, as the computer desperately tries to complete the condition you gave it. As a computer example, if we try to have a program terminate when an integer i is no longer greater than 99, but i is initially 100 and only increases,
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the loop will never terminate and the program will crash. To avoid these, you generally want to think through the flow of your code before running it -especially with loops- to make sure that all of your statements can be completed by the computer. Carefully planning out your code before you begin writing it is an extremely useful practice, and something we’ll be covering towards the later part of this video. The final type of error that we will be covering is a logic error. This error is also pretty self-explanatory. A logic error occurs when the code runs smoothly without any runtime or syntax errors, but the result that you get isn’t what you wanted. For example, let’s say you had a calculator app, and you wanted to instruct the program to add two numbers, except it multiplied them instead because you used the multiplication symbol on accident. This leads the sum to be 36 instead of 13. Nothing went wrong with the code syntax or runtime wise, the code runs just fine, it just doesn't work as you intended it to. These are often the hardest types of errors to debug since most of the time, you’ll
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have no idea why the code isn’t working, and certainly not any idea of how to fix it. This is why it's a good idea to test your code incrementally, don’t wait until you’ve been programming for an hour before testing your application, or else you’ll run into a lot of logic errors. Logic errors can be extremely frustrating and could cost you a lot of time, making them a huge pain, but if you know how to effectively debug your code, you’ll be just fine. Speaking of debugging your code, that brings us straight into our next topic, which is how to debug your program. Now, let’s say you have written a program. You think it's ready, and you’re ready to test it. You’ve been working hard on this, and you’re excited to see it in action. You run the program, and wait for it to run smoothly and efficiently. Only, it doesn’t work. You have encountered one of the three errors we just mentioned. You really want this code to work, but how? This is where debugging comes into play. If the code is giving you an error, then the first thing you should do is read the error. Oftentimes, for syntax and runtime errors the IDE will print an error message out to the console. See what line or lines it points to- since those will be the lines in which
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the error occurred- and see if you can understand and fix what it says the problem is. If the error isn’t clear, or you’ve never heard of it, then try googling it, there are many websites out there such as stackoverflow which serve as forums to ask and answer problems with code. Chances are, if you’ve had a problem, someone else has had the same issue and there is likely a tested solution. Usually, when a syntax or runtime error pops up, you should be able to find a fix for it fairly easily; however, as I said before, the issue may arise from some loophole or oversight in the code you hadn’t planned for beforehand. Maybe you did something as simple as multiply two variables instead of adding them. These are the logic errors we talked about previously. These problems usually won’t have red text show up to explain to you what went wrong. You’ll have to figure it out yourself. Now there are a few different strategies you can use in order to track down and fix a logic error. First, you can use print statements and the console in order to determine where the code is going wrong. Imagine you have a conditional statement that will run one segment of code if an integer
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x, is greater than 5, and will run another segment of code if not. If, in your program, x is supposed to be greater than 5 when the program reaches this conditional but for some reason the program is still printing out “X is small” you could use a print statement to help. For this problem specifically you could place said print statement before the branch of the conditional that would print the value of x. Now when you run the program you know exactly what the computer is thinking. Printing out the value of x just before the if/else statement will let you know if the variable has the value you want it to have, and if it doesn’t you know that somewhere above that conditional something went wrong and x was set to a value you didn’t want it to. In this case, x is equal to 2, which is why x is small is being printed out. Now we know what the problem is we can track down where and when in the code we modify x to figure out the problem. Use print statements to determine where your program goes wrong, and then try to track down the cause of these issues and solve them. If you use this strategy, make sure you end up deleting the print statements afterwards to avoid clutter in the console.
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The situation described above could also be solved using a breakpoint. A breakpoint pauses your program when the line you placed the breakpoint at is reached in your program. If, say, you would like the program to run through a certain conditional and set a variable based on that conditional, but you are unsure if this actually happens correctly in your code, you can place a breakpoint inside the conditional path you want to run. Upon the breakpoint being reached, the program will pause, and wait for you to continue it through a button press. This signals that the spot in the code where the breakpoint was placed, in this case the correct conditional path, has been reached by the program. You can then continue the program knowing that was or wasn’t where an error in your code occurred. Breakpoints can be used in conjunction with print statements in order to both pause the program, and perhaps view the values of your variables at the moment in time to give yourself all the information you could want. You can also have multiple breakpoints to help slowly work through your program and determine where the error has occurred. A combination of these two strategies will help you easily determine where in your code you have incurred a logic error.
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Next, let’s go over what to do if you think you have tracked down the section of code that causes the problem. You may think you should delete it, but it’s likely you put it there for a reason, and you don’t want to lose that work if you don’t have to. Firstly, try commenting it out. Comments are used to markup code and explain their surrounding sections, but they can also be used to debug. Anything that is designated as a comment will not be read by the program as code, and will be skipped over. Essentially, it becomes something that is only there for YOU the programmer to read. The syntax varies from language to language, but it usually involves placing some symbols before or around the code you would like to be commented. Examples of how to comment in different languages can be seen on the screen now. Also, when you comment something, the IDE will grayscale the line of code, making it extremely easy to determine what’s commented and what is not. Commenting code ‘deletes’ it in the computer’s eyes without actually deleting it. If a problem is present before you comment a section of code but it is gone afterward, then that section of code is the culprit. If you comment part of a code out and there are still issues,
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then move onto another section until you find the culprit. Once you do, you can tweak it until it works as intended or delete it entirely and you will have a fully functioning program once again. Hurrah! Now that we’ve talked about what to do IF you’ve encountered an error and a strategy on how to find and fix it, I’d like to talk about some strategies you can use to AVOID errors in the first place. Firstly, backup your code frequently. In the event of the code completely bugging out and you being unable to fix it, you will want the ability to revert to a previous version where the code was still working. If you save frequently enough, then you will probably not lose too much work. Version managers like Github or Subversion can help with this, as they backup code to an online cloud service in which you can easily pull previous versions of the program at any point. Also, on top of saving, run your program frequently to ensure that the current version works as intended. This accomplishes two things. First of all, it prevents you from saving a backup that doesn’t work. Secondly, if you encounter a problem, it will be easier to find if you have only made a small number of changes since the last time you ran it and it worked, and
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thus you will only have to look through the new code for problems. If you’ve spent 5 hours coding and hadn’t run it during that time period, it’s going to be extremely likely that at some point during that 5 hour code sesh you messed up, and it’s going to be even harder to figure out where you went wrong. Errors, while annoying and extremely frustrating, are a fundamental part of making you a better programmer. Alright, now that we’ve covered errors for a bit, let’s hop on back to programming statements and talk about one of the most important concepts in computer science, the function. Now, you may not know it, but we’ve actually been talking about a few functions this entire series. Print statements, for loops, and even basic math operations are all examples of functions, which of course begs the question of what actually defines a function. Well, a function is a segment of code that can be easily run “calling” the function name and depending on the type of function, will do something in return. Functions can be called numerous times, and in numerous places. Essentially they are like wrapping up a segment of code into a nice present and giving it a name which; when called, will unwrap the present and go
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through the code you wrapped up. For example, the print statements we have been using this series allow us to print something to the console any time we want are functions. You see, we just “call” the print function and enter in what we want to be printed to the console, and the computer does it for us. Behind the scenes, there is actually even more complex code that is in charge of taking your text and translating it to the console to be printed. The developers of almost all programming languages realize that you don’t want to program something that manually has to print something to the console through the use of complex programming, and so they implemented the print statement to reduce the stress and complexity of code on the user, abstracting it down to a simple line of code. All of that code that is used to print something to the console is wrapped up like a present and given to us in the form of one line, “print()”. This is actually the main theme of all functions and the backbone of any good program. Oftentimes in your program there are going to be sections of code which are repeated and serve the same
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purpose, or equations which you want to allow differing inputs of. And so you can use functions in order to condense these down into singular lines of code to save both time and reduce clutter on your code. As you will see soon, functions are EXTREMELY powerful and will definitely be something you utilize all the time in your computer science journey. The print statement is just one example of functions in everyday code. There are thousands of functions that are available to you through IDE’s. However; because you won’t always use all of the thousands of functions that are open to you in a single program you have to import these functions from packages found in the IDE, which is something we will cover later on. Now, there are four main types of functions in most programming languages, and they are separated by two defining features: whether or not they take in arguments, and whether or not they return values. Let’s start by separating them by whether or not they take arguments, but first we have to cover what arguments are. Arguments are essentially variables that we pass into the function in order to be manipulated
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and then either returned back to us, printed to the console, or used in another operation. Think of functions with arguments like ordering food at a restaurant. If you walked up to your local five guys and told them you wanted to get food without supplying a type of food, they would probably look at you confused. You need to tell them what exactly you want to order so that they can give it to you. In this case getting food is the function and what you order is being passed in as the argument. Based on what you tell them, or the argument, they will do something different. You also should note that the argument can be many different things, it could be fries, burgers, soda, anything really on the menu, and such is the case with arguments in programming. This is essentially what happens with the computer, for example, the max function which takes two integers as arguments and returns the maximum number between the two. Now, for
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this function if you don’t input two numbers or variables for it to compare, it's going to throw you an error just like the five guys employee, he doesn’t know what you want to eat since you didn’t provide him any arguments, and the computer doesn’t know what two numbers you want it to compare and return since you didn’t provide it with two integers. Arguments are a way for programmers to have one function that can do many different things depending on whichever variables can be passed through. Arguments add variability to programming and can help diversify your code. Thinking back to our five guys example, a restaurant that only allows one type of food to be made regardless of what you order isn’t going to be very useful or diversified, but if we’re able to pass in arguments and tell them what food we want, our experience can be heightened and more options become available, which is exactly what happens when you accept arguments in your functions. Now that we’ve talked about functions that take in arguments, let’s move on to functions which do not take in arguments, because functions can also be created and used without taking
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in arguments and still be incredibly useful. For example, let’s say you were making a text based RPG game and one of the options you give your player is the ability to view their stats at various points throughout the game. Now every time you come upon an option and they choose the “View Stats” button, you don’t want to have to type out 6 different print statements for every statistic they may have, your code would get cluttered and messy very quickly. Instead, what you could do is package the 6 different print statements in a simple function called printStats(). You don’t need to pass any arguments into the functions since the function will do the same thing no matter what the statistics on the player are. Now, everytime the user wants to view their stats, you simply call the printStats() function and voila, the user’s stats are printed for them to view. This allows you to save a lot of time writing out code, but also a lot of space which is extremely important when your programs begin getting into hundreds and thousands of lines and you want to easily search through it.
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Okay, now that we’ve separated functions into those that take arguments and those that do not, let’s again split these up into those that return values and those that don’t. Now the thing you have to understand is that when you’re making your own functions, which is something we will be covering soon, you have to choose what your function will return, if anything at all. Functions are able to return values back to the user whether they be String variables, integer variables, or even arrays. Now the thing to note about returning values is that calling the function alone won’t do anything. You have to return the value into something. As an example, the Max function we talked about previously would return an integer, but in order to do something with it we would have to either set a new integer variable equal to the result of that Max function, or we can print out the result of a function, which in this case would just print out the maximum value between the two integers. Using functions which return values don’t do much on their own, you have to
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pair it with something in order to gain use out of it. Let’s do another example, let’s say you had created a function which took in two string variables as arguments, combined them using that fancy String math we talked about earlier, and then returned them as a single string. This combineString function could then be used to create new String variables since what it is returning is technically a string. The variable would simply be set to whatever is returned from the combineString. The last type of function is one that does not return anything, and these are known as “void” functions. Oftentimes these are like the printStats function we created earlier, simply used to condense large amounts of print statements that appear often in your code. These cannot be set to variables since they don’t return anything and just get the code within them run through. So there you have it, the 4 types of functions. Ones that take in arguments and return things, ones that take in arguments and don’t return something, ones that don’t take in arguments
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but still return values, and the ones that take in arguments and don’t return anything. Each of these 4 types of functions are useful and unique in their own way and you will probably find yourself using them all throughout your programming journey, so get used to the different types of functions and know how to make the most of them, as they are all extremely powerful. Finally, I’d like to talk about one of the major benefits of functions, which is that it makes it super useful to make large changes to your code without having to go through the entire program. Each function call is just a copy of that function's original code, and so it’s very easy to make changes to the function and have it translate to across your code. Let’s go back to our printStats() function and say that you wanted to go back and add in a new stat that the player can level up through experience in the game. Without functions, you would have to go back into your code, find every instance that you had printed out the users stats, and create another print statement to display the new statistic. However, if you had created a printStats() function like we did a little while ago, all
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you would need to do is find where you defined that function and add in a print statement which displays the new statistic and you’re done, bam. Now, every place which had called the printStats function previously will now also print the new statistic as well. You can see how powerful functions can be if used properly, and we haven’t even scratched the surface yet. Now, up next we’re going to cover how we can import other people’s functions that they’ve written and use them in our code. Now before we get technical, close your eyes and imagine you are trying to build a house. Sure, you could grow your own trees, chop down your own wood, make your own tools and nails, and build it up from scratch. But why do that, when you can simply go to your local Home Depot and buy these materials that others have already made ready for you. That’s the main idea behind importing functions into your code. Importing functions allows you to gain access to libraries of functions that other people have already made for you. This is just as useful as it sounds. There are so many functions that are super useful for any given program that it would take you forever to write them all yourself. Luckily, other
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people have already done most of this for you. In each programming language, you are able to use an import statement to import libraries of functions into your program that you can use as you write it. A library is simply a collection of functions that all have the same theme. It may be a math library, a data analysis library, a library which translates text, or anything that you can think of really. There is such a variety of libraries for any given language that most functions you require that are not hyper-specific to your program can likely be found in some library. In fact, a good portion of any programmer's job is looking online for packages which can make his or her job easier instead of handwriting functions. Now, I can hear you saying, “Wow, that’s sick, how do I do it?” Well, it’s quite simple: an import statement. In most languages, an import statement consists of 3 parts. The library you would like to import from, the package you would like to import from that library, and then which class from that package you would like to use. For example, we could load up the Java library,
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and from there import the util package, short for utilities, and then from that utilities package import the scanner class, a class which allows us to read information from the user. A package is simply a smaller sect of functions and methods to help differentiate between the thousands of methods contained in a library, and class is even more specialized than that. Now if you don’t know what specific classes you’re going to want to pull methods from, you can use a star * to import all classes within the package you’d like. However, it can be beneficial to be more specific, and only import the classes you would like, as it helps with efficiency of the program in the long run. For instance, in python, the syntax to import a library is import followed by the library name. However, importing an entire library is more computationally taxing than importing specific functions from a library. Imagine you would only be using the factorial function from the python math library. It would be a waste of computing power to import the entire library, and would increase
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the load time for your program. For smaller programs, this isn’t a big deal, but it really starts to add up when dealing with larger projects. Therefore, you would instead use “from math import factorial” or the java equivalent “import java.math.factorial”, and now have access to that one math command only. This limits the functions that you can use, however it saves programming runtime. If you decide you want to use another function that you hadn’t planned for, you can always go back and import that too. Many times, if you try to use a function from a common package and you have not yet imported it yet, the IDE will prompt you to do so. If you’re trying to figure out which libraries you want to import, think of the functions you’re going to need in your program. Perform a simple google search, and you will probably run into a package or library that already exists in your IDE that you can use. And if you can’t, there are ways to download and import additional projects to fit your needs. But if after all of that you still can’t find a library that contains the function you are looking for? Well that’s a perfect segway into what we’re going to talk about
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next, which is the basic structure for writing your own functions. So at this point we’ve talked about both what functions are and how we can get some very useful functions by importing functions through packages. But there are definitely going to be moments in your programming journey where you’re going to want to make your own functions because you want to make one specific to your program and code. Luckily, making your own functions is extremely simple, there are just some basic rules I want to cover. Now while we’ve previously used making functions as an example for other topics such as the playerStats function from a little bit ago, they were extremely abstract and didn’t go in depth into what is needed for an actual function to operate. So right now we’re going to be covering a skeletal system of everything that needs to be included in a function to get it to work. Now think back to the 4 different types of functions that we talked about previously. Functions that do and don’t return values and functions that both do and don’t take in arguments. For creating your own functions, we’re just going to go down the list and talk about how to approach creating them, starting with the most basic of the bunch,
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one which takes no arguments and returns no values, but before we start that, there are a few small things I want to note about function naming conventions. The variable naming conventions we talked about previously also translate over to function names. So you can’t have two word functions and you can’t use special characters like periods or commas. Generally you’re going to want to follow the same camelCase style which we talked about in the variables video. Alright, so in general for making functions, each language differentiates how you tell the computer that it's a function. In java you have to define the functions scope, which is something you don’t really need to know unless you’re going to become more invested in java, but basically it tells the computer which parts of code can use the function and which type can’t. For this series all of our functions are going to be public. From there you then determine which type of function it is, so in this case since it won’t be
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returning any variables we’ll just put void to signify this type of function will not be returning anything. Finally, you put the function name after those two identifiers along with a set of parentheses after it like so. The parenthesis are where your arguments would go if you were making a function that took in arguments, but since for our first type of function we’re not incorporating arguments into this function, let's just leave that blank. All of that is just for Java; Python on the other hand all you do is put def, short for define, and then the function name with a set of parenthesis. So as you can see, each language is going to be different, but the main thing we want to remember is to always add parentheses. From there, we just type what we want our void function to do within the confines of the function and then close off the loop and we’re done, easy peasy. In Java, the confines of the loop would be whatever is contained within the curly brackets, and in python it would be until you are no longer indented. At its core, this is the most primitive type of function we’ve just made. Something which takes in
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no arguments and returns no values, quite similar to the printStats function from earlier on. Moving on to the next type of function, creating a void function that takes in arguments. Now this process is going to seem very similar to the previous except for one small adjustment. Remember the parenthesis that I mentioned like 30 seconds ago, well we put any variables we want the user to pass into the function into these parenthesis, and then when we “call” that specific function, it will be required to have those variables passed into it. For example, in Java, let’s make a function that takes in 2 numbers and prints out the product of those numbers. We start with the public void plus name of function setup since again, we won’t be returning any values. And now comes the new part. Inside the parenthesis, you define which type of variables you want to pass in as arguments, in this case an integer, and then a name for that variable. This name is what you will use to refer to the integer the user passed in. For this example let’s just call it num1. Then if we want to add
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another argument, we simply add a comma in between the two and we can make another integer variable num2 to hold the second number. We could do this for however many variables we want to pass into the function, but for now let’s close off the parenthesis and just print the product of num1 and num2. As you can see, we refer to the two numbers the user will input to the function as num1 and num2. Now, whenever we want to call the multiplyNumbers function, we just have to make sure that we are putting 2 numbers in as arguments. In this case the number 5 becomes num1, and the number 8 becomes num2. From there we simply run the code and the number 40 is printed to the console. It’s important to note that you can also mix and match variables when making arguments. So you can have someFunction which takes in a char, an integer, and two strings all within one function. Pretty neat in my opinion. The last thing I want to mention
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about arguments is that when you call a function you have to follow the variables you defined when making the function. So for our multiplyNumbers function you couldn’t put in a string and then an int. It HAS to be two integers because that’s what the computer is expecting to be passed into the function. So now that we’ve gone over how to make functions that don’t return variables, we have to cover those that do, and we’ll start with ones that don’t take in arguments. Now the main difference between defining functions that return variables and defining ones that do not is that in some cases you have to specify that you want this function to return an integer variable, this is most commonly used in Java, where you would replace “void” with “int” to tell the computer that you want this function to give something back to you in the form of an integer. This works the same as if you wanted to return a string, char, or even an array. You simply replace the word after public with whatever variable you want to be returned by the function. The most important thing to remember about making functions that return variables is
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that no matter what path your code takes, it MUST return a variable NO MATTER WHAT. What does this mean? Well let’s say you had some String function in a game and inside of it there was an if statement where if the player score was above a 10, you returned a congratulatory message. This works fine if you print the result of this function and the player’s score is above 10. But, if the playerScore was less than 10 then you don’t enter the if statement and then you don’t have something prepared to be returned to the user and so the function is going to throw you an error. You HAVE to have all your paths covered which may seem simple, but if you’re making a function with a switch statement in it containing high amounts of cases, this can get out of hand quickly. Something I like to do just to make sure this doesn’t happen is put a return statement at the bottom of the function with a string or an integer so unique that I’m able to tell that the code is not running properly and can fix it. The main point I’m trying to get across however,
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is always cover your exits and always have a return statement prepared for any case the user may throw at you. Another small thing to note is that you can’t return one type of variable if you have already defined the function to return another type. For example you can’t return a string in an integer function or vice versa. The return statement must always match the type of function no matter what. The final type of function is one that returns variables and also takes in arguments, and for these all you need to do is combine what we’ve learned from the previous cases. First, you assign your arguments in between the parenthesis, making sure you have also defined what variable you want to return, and then ensure that no matter what path the code takes that you are always returning that variable type. That concludes our discussion on functions. As you can probably tell, functions are an extremely vast subject area and require a little bit of practice to fully understand, which is why later on we’ll recommend some websites you can use to practice these more difficult topics.
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Now I’d like to switch gears a little bit and continue our discussion from earlier on arrays. Arrays, while useful, aren’t the only way to store and manipulate information. In fact, there are a multitude of different ways to store data in computer science including LinkedLists, Stacks, Queue’s, Maps, Trees, and many others too. Right now; though, I’d like to talk about 2 cool, wacky and zany ways to store data that we haven’t previously covered: ArrayLists and dictionaries. But before we get into those, let’s get a little review/reinforcement of array’s. As you may remember, arrays are basically lists of values that are stored together. When you initialize an array, you give it a size, and this size is fixed. You won’t be able to increase the size of the array, so when you make an array, it’s length is final. To access the values in an array, you reference them using an index which starts at 0. What this means is that the first item of an array is not at position 1, it is at
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position 0, and it’s position is commonly referred to as it’s index location. So, to find the nth item in an array, you would refer to it as index location [n-1]. However, as the size of an array is fixed, you have to be careful to not reference a position that is beyond the total size of the array, or append too many items to it, as this will return an error. We also have what are known as two-dimensional arrays, which is an array containing an array at each of its indexes. Or, you could have an array containing arrays containing arrays containing arrays containing arrays, depending one what you’re trying to do. Multidimensional arrays can be useful in more advanced programs for organizing a wide volume of related values. If that’s confusing at all, skip back to earlier for our full discussion on Array’s, the time-stamp will be in the description. Now that we’ve reviewed array’s, let's go over array lists. Array lists (or just lists, in Python) can be thought of as a growing array. Earlier, we mentioned how you have to be careful to set an appropriate size of your array and
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make sure to only reference and append values such that you remain within the size of the array. However, with array lists, this isn’t a problem. After you initialize an arrayList, it instinctively has a size of 10, but if you append a values such that the size of the arrayList goes beyond 10 elements, an arrayList will “grow” itself, meaning that the computer will allocate more memory to the array to increase its total size so that the new values can be appended. This is quite useful when you don’t know the exact number of values that the array will need to store, or want the ability to store values to your heart’s content, such as making a database with an unknown amount of user’s that will sign up. There is a lot more to uncover when regarding arrayLists, but for this surface-level series, that is all you pretty much need to know, so let’s move on to dictionaries. Now when we talk about dictionaries, we’re not referencing that thick book you probably have lying around your house which has thousands of definitions. In computer science, dictionaries are like arrays, in that they store multiple values, however their values are stored very
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differently. Rather than being referenced by their position within the dictionary linearly, each value is tied to another value that is used to reference it, or its “key”. Because of this, we need to throw away all conceptions of dictionaries as a linear way of looking at data, since in actuality it is much more fluid and interchanging. Basically, we say that each position in a dictionary holds a key/value pair. When referencing a value in a dictionary, you will use it’s unique key, and the dictionary will tell you the value that is tied to it. Think of it like this, each time you add an item to your dictionary, your computer creates a handcrafted box to store the data, and also custom-makes a jeweled key, one of a kind, no other like it in the world. This way, there is only one key that goes to the box that stores a certain bit of information. Because each key must be unique, reusing a key in a dictionary will result in an error being thrown because having two keys that are exactly the same would confuse the computer as to what box, or bit of information, that key leads to. However, you can store the same value in multiple key/value pairs,
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since the keys would all be different. Now like I said, dictionaries are more fluid, making them easier to organize than arrays, as everything is set up in a more logical manner. That is to say, it is easier to find the value you are looking for when you are using keys rather than simply referencing their positions. Let me explain what I mean. Imagine you have a dictionary of prices at a store where the key is the name of the product and the value is the price of the item. Maybe apples cost 1 dollars, milk costs 2 dollars, and bread costs 3 dollars. You can see that in the dictionary, each key is the name of a product, and each key corresponds to the price of each product. So to find the price of bread, all you need to do is simply call the dictionary using the key “bread”, and the dictionary would return the value 1. This makes it extremely easy to track values through your code since you’re working with tangible values rather than numbers which don’t mean anything to you. You can also manipulate dictionaries in many the same ways you can manipulate arrays and array lists. You can iterate through a dictionary and perform many operations and comparisons on the values. If you want to find the product with the highest price, for example, you can
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iterate through the dictionary to find the value that is the highest amongst the grocery store items. Arrays, arraylists, and dictionaries are useful in their own right, as are the mass amounts of other ways to store data, and each boast certain advantages over one another. We already covered the basics of 3, but since there are so many, we don’t have time to go in-depth into each and every one of them, and so in order to help you grasp the basics of storing information, we’re now going to talk about one of the most important functions needed to understand arrays, which are searching algorithms. Now, just as there are many ways to store information in computer science, there are even more ways of searching through lists. Searching algorithms at their core are ways in which we can look through a list of values stored in an array, say a patient name list or a high score list, and find a particular piece of data. The goal of a searching algorithm is to simply give the algorithm a string or object you want it to find and return the index of the array that contains that string or object as fast as possible. Now this may seem simple, but lots of software runs on the backbone of being able to search through
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lists extremely quickly, making searching algorithms, and in particular efficient searching algorithms, an important topic to cover. Additionally, this is the main functionality that arrays are used for and is the backbone of many of the methods used with arrayLists as well as many other storage methods, so knowing them will take you a very long way. Typically searching algorithms are used to return the index of a particular data point so that it can be used, modified, updated or checked on. For example, if you are about to check into a hospital run on an array system for patients, the staff must search for your name in the database and by returning the index of where your name is, they now have a quantifiable number that they can use to easily check you in, rent out prescriptions, schedule you for checkups, update your personal information, etc. without having to search through the list for your name every time. You may think that there is little difference between searching algorithms, since computers nowadays can perform millions of calculations per second, but when you’re a huge multi-billion
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dollar corporation trying to find a certain data point in a list containing thousands or even millions of data points, small differences in efficiency are going to make or break the user experience. Even a 1% improvement in efficiency can mean big differences in the amount of time a user is waiting for a simple task. Now before we jump into different types of searching algorithms, we must discern between the two states that arrays or lists can be in, either sorted or unsorted. A sorted list of information is characterized by some sort of rankable value, whether that be a patient ID, credit card number, or even by alphabetical values like username’s or legal names. An unsorted list is just some random assortment of related information, not sorted by any particular order or reason. Some searching algorithms only work for sorted lists, usually the more efficient ones, and some work for both sorted and unsorted lists, although these are usually less efficient. If you end up pursuing computer science further, you will have to deal with both sorted and unsorted lists, so it's good to know common searching
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practices for both Another thing to note is that we determine the efficiency of a searching algorithm based on both the worst case scenario and the average number of items it must search. We call this Big O notation, in which each searching algorithm has an equation which takes in the size of the array as an integer n, and will output an worst-case scenario efficiency value that we can use to compare with other searching algorithms. We can then also look at how long; on average, it takes to find an element in a list. Using these two methods allows us to easily compare how efficient two algorithms are. Alright, now that we’ve got some background on searching, let’s hop right into it. The first type of search we’ll be talking about is called a linear search and you’ve honestly probably used this multiple times throughout your life. Every time you have to search for your name on a list of people you probably follow the same pattern. You start at the top, check to see if the first name on the list is yours, if it is. Great. If not, you move on to the next name on the list until either you find your name, or you
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don’t in which case you leave. A linear search works the same way, you start with the first element in the list, compare it to the value that you’re trying to find, and if they’re the same you’ve found your match and return the index of that element, and if not you move on to the next element in the list until you either find the thing you’re searching for or you run out of list to check. Seems pretty simple right? This is because linear searches are pretty bad when it comes to efficiency, especially in the worst case scenario. If the item you’re searching for in the list is the last element, you’re going to have to check the entire list of items before you find the one you’re searching for. On average; however, you’re going to get it about halfway through the list. This makes the linear search O(n) worst-case scenario, since in the worst possible case it will take the entire length of the array, or n, to find the correct value. The linear search on average will return the correct index in O(n/2) or halfway through the list. The linear search is great; however, since it can work with both sorted and unsorted
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lists, because of the fact that it will eventually cover every element in the list. The other search we’ll cover requires the list to be sorted which may seem like a drawback, but having a sorted list allows you to use algorithms that are far more efficient than the linear search. So overall, the linear search is a good basic searching algorithm for if you have an unsorted list, but if your list is sorted, there are way more efficient options out there for you, such as the binary search which we’ll be talking about now. The binary search uses a recursive process to break the data in your list down into more and more manageable bytes, taking advantage of the fact that it’s sorted, in order to find the item you’re looking for faster. This one is much harder to wrap your head around so let’s start with an example. Let’s say you have a list of 10 names sorted alphabetically, like shown on the screen now, and you wanted to find your name within that list. In binary search you would first look for the middle-most name, in this case the one at the 4th index. Just a quick aside, since there is no “true” middle, the computer automatically uses the
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next one down as the “middle” value. Now, once you find your middle value, you first check to see if the name you’re searching for at the index you’ve chosen, if it is you simply return that index, but 99.9% of the time it’s not including right now, so let’s keep going. If the value at the middle index is NOT equal to the one you’re searching for, you check to see if the value you’re searching comes before or after the middle index. For example, if you were looking for the name Brendan and the value at the middle index was Carl; Brendan obviously comes before matthew alphabetically and since we know the list is sorted, what we can do now is ignore the entire bottom half of the list and just focus on the top, since we know that if Brendan is even in the list, it’s going to be in that top half. Now, we simply treat the top half of the list as an entirely new entity and repeat the process over again. Again, we would find the middle-most element of this
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new list of names and again compare it to the name you’re trying to find. If it’s the name we’re trying to find, we return that index, but if not we compare to see if it comes before or after the middle index. Going back to our example, let’s say the middle index of this new list is AJ. Now, we know that Brendan comes AFTER AJ alphabetically so we can now ignore the top half of the list since we know that Brendan is going to be in the top of our list. Now we repeat this process again and again until we find the name we are looking for. So for our example, the middle index this time is Brendan, and that’s what we’re searching for so we finally would return index 2. In binary search, eventually the index we compare to our search term will be the same and once it is, we can return the index and move on. Now if we don’t find it, which happens after we have eliminated the entirety of the list without finding our search term, the algorithm will simply return a null value to let you know that the item you’re searching for cannot be found in
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the list. The binary search is way faster and more efficient than the linear search since we are drastically cutting down the amount of elements we have to look at, making the program run faster. In almost 99.9% of cases in which your list is sorted, the binary search is going to return a result faster than the linear search, so if you have a sorted list, your best option is to go binary. As for efficiency, the binary search is O(log n) for the worst case scenario which can be confusing if you don’t fully understand logarithms, but all you need to know is that it is way more efficient than the linear search. It’s average scenario is actually also O(log n) as well, which again is infinitely times more efficient than linear. Now, while there are other types of searching algorithms you can use, these two are the most common for both unsorted and sorted lists, so we will stop there for now. Up next, we’re going to be covering one of the most confusing and important topics in computer science,
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recursion. Let’s start with the most important question: what exactly does recursion mean? In programming, recursion refers to functions that repeatedly call themselves. Meaning, that in the instructions that occur within a function, one of the instructions will be a call to that same function you’re already in.In the extremely primitive example on your screen now, you can see we have some function which, in the confines of itself, calls itself. A recursive function will usually take into account some integer as an argument, and will use this to carry out some instructions, modifying the integer that was entered, before calling itself again with that new integer as its argument. To better understand these functions, let’s discuss the basics of how we go about programming one of these recursive functions and create one ourselves. A really good easy example of a recursive function is one which sums all numbers from 1 to n, so let’s make a recursive function that does just that. The first thing we need is the actual function, and we’re going to make it an integer function which takes in an integer n as an argument. The reason we do this will be explained later but for now let’s move on to the base case.
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A base case is simply a definite value which all recursive statements, the ones that are being repeatedly called as we go through the function, try to get towards. At the beginning of the function, we test the value that was passed in by the argument against the base case to see if it is satisfied. Usually, these base cases are some requirements, like if n, as I described before, reaches a certain value or is equal to a certain value. It is extremely important that the base case is set to some requirement that n will eventually meet for the same reason that it is important to avoid infinite loop: we do not want a stack overflow error to occur. For example, if our base case was to stop calling the recursive function when n was greater than 100, and if it is not, we call the function again but with n-1, and we started with n as 99, we would never reach the base case and the recursive function will repeatedly call itself over and over and over again, subtracting 1 from n and hoping that somehow it will eventually be greater than 100 until your computer crashes,
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not fun. So anyways back to our recursive sum example, let’s make our base case when n is less than or equal to 1. This way, we can start at some positive integer n and subtract from it until it hits at or equal 1, in which case we can exit the recursive statement. Cool. Now, if n is not less than or equal to 1, what we want to do is return the SUM of both n and then the returning value of our recursiveSum method minus 1. Why do we add n + the function call? Well let’s actually go through the function as if we were the computer and see why. We start with a call of recursiveSum with n = 3. We know that 3 is not less than or equal to 1 so now we try to return a recursive sum of n (which is 3) and the returning value of recursiveSum with an n of 2. We don’t KNOW what the returning value of recursiveSum with an n of 2 is so we have
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to go through the function again, only this time n is 2.Again n is not less than or equal to 1, and so this function will go into the else statement and return…2 plus ANOTHER recursive statement, in this case the returning value of recursiveSum with an n of 1. So once again we have to go through the recursiveSum function to get the value that will be added to 2 and then returned and added to 3 and then returned. Hang in there we’re close. Now in this function, n IS less than or equal to 1 and so we return n, which is 1. Now we take that n, which is 1, and that is what gets added to 2 in the previous function call and then returned, so this would return 3. Now this 3 is what gets added to the first function call, which is three, and so it becomes three plus three which is 6. And FINALLY after
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all that time, we get 6 returned from the function. Which, if you’ve been following along at home, 3 + 2 + 1 is indeed 6. Now this may seem like a waste of time since 1 + 2 +3 is not a hard operation. But to those of you saying that I ask you to please give me the sum of all numbers from 1 to 3,567. Godspeed. Now recursion is a VERY difficult concept to wrap your head around, so if you’re not 100% comfortable with it at the moment, please rewatch this section of the lecture to better familiarize yourself with it. Alright cool, now that we have a little background on recursion, let’s talk about why it works so well. Now to understand why and how recursion works, we must first understand what a stack is. A stack is a data structure that contains all of the tasks you instruct your program to complete. Based on a certain method, your program will then carry out the tasks you give it. It’s called a stack because if we call start another process before the previous one completes,
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the process is “stacked” on top of the other one such as the animation on your screen is showing now. Programs we write will follow the LIFO structure. For those unfamiliar with accounting, LIFO means last in first out, or the last item put on the stack will be the first one removed from it. Essentially, every time you ask your computer to complete a task, that task is added to the stack, and will be the first one to be resolved. Think of it like a stack of stones, you can keep adding stones on top of your pile, but in order to get to one near the bottom, you first have to remove all the rocks on top of it. Now when your function continually calls itself without end; without a base case, like in our infinite loop example then the stack will never be resolved, as items will be continually added to the stack without any of them ever being completed. In this case, the memory allocated to the stack is exceeded, and a stack overflow error occurs, resulting in your program crashing. Think of this as if you’re doing chores
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and before you complete one chore, you get called to do another chore, and then before you can complete that one you get called to do another one. Since you keep stacking tasks or chores on top of each other, the stack of tasks will never be completed and you will probably die before ever finishing any of your chores. This is the same logic that makes infinite loops crash your program. Recursion works on these same principles. The initial call makes a second call which is added to the stack, and now that one must be taken care of first, but in that one another function is called which gets added to the stack, and so on, until you reach the base case in which you slowly start going back down the stack. In conclusion, recursion in general is extremely useful because by calling the same functions repeatedly it breaks down the problem into smaller sections, and results in the program being more efficient. Small parts of problems are easier to solve and less taxing to compute than the entire problem at once, and the computer can combine these small solutions into the
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main solution in the end. Now as we wind down our introduction to programming series, we want to take some time and go over some of the soft skills needed to be a successful computer scientist since it’s not all about writing code. In fact, many professional computer scientists will tell you that the majority of their job is spent thinking about code rather than actually writing it. This is because much of programming boils down to problem solving. How do we optimize this system, how can we make this feature for our app? What type of movement do we want for our game and how can we program it? The harsh truth is that no good program has ever been written simply from the programmer getting the prompt or idea, sitting down, hopping on an IDE, and starting to write code. There are many tasks we should go through beforehand in order to plan out our code so we ensure that when the time comes to program, it’s a clean and easy process, and not riddled with mistakes and bugs. This is where pseudocode comes into play. Think of pseudocode like this, if you wanted to take a family trip to the grand canyon, would you simply hop in your car and drive off and figure things out later? No, because
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that would be ridiculous. Instead, you would spend some time planning out the trip, what sites or places do you want to visit? What hotel reservations are you going to have to make? What kind of things are you going to do when you get there? What routes or highways are you going to take and why? All of these things must be determined out before you can even think about hopping in your ford explorer. So how does this translate to pseudocode? Well, think of our family trip to the Grand Canyon as a program. Programmers use pseudocode, pseudo meaning not real, and code meaning, well, code, as a means to plan out their programs before they write them, just like how we planned our trip before going. They throw away syntax and naming conventions for variables and just focus on what they want the program to accomplish, and how they plan on doing that. Pseudocode is very similar to constructing an outline for a paper you’re writing. You write down the main topics of the essay and plan out your major talking points, but you don’t worry about the nitty gritty details of it all such as word choice, grammar conventions, and proper formatting. By doing this, we allow
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ourselves to think freely and not worry about stressing the small stuff. At least not yet. Alright, so now that we know WHAT pseudocode is, let's talk about HOW we write pseudocode. You see, the best part about pseudocode is that it can take the form of many different things for many different people. Each computer scientist probably has their own methodology for planning out their code, and since there are probably hundreds of different methods of writing pseudocode that are out there, today I’d like to focus on 3 popular ones that I think you might find to be extremely useful. The first of these are known as flowcharts, and mainly they can be used to think through the process of a particular function. A flowchart is fundamentally a graphical representation of a function and how it might flow. Many programmers do this, and lay out the conditional statements and loops they want as different blocks in the flow chart, connected by arrows and charting out every path of their function. From there, it’s extremely easy to create test cases and follow them throughout the flow of the function through the different blocks and arrows. For example, we could have a flowchart that goes something like this.
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A user enters a number, and if this number is 8, I want the program to return True; however, if the number is not 8 then I want to return false. It’s a great way to visualize what the function’s overall purpose is and also look for any errors that you may have missed when thinking about the function, such as a missing path. It also abstracts the programming statements up to simple blocks, making it easier to modify or change completely. The best part is, that when you have finished testing cases you can simply convert the blocks into statements and you have a well-written function without any debugging. Another popular pseudocode technique that is used often is to simply write out what you want your code to do chronologically. Don’t necessarily think about what programming statements and functions you want to use, just jot down, from start to finish, what it is the program you are writing is going to do step by step. For example, let’s say you’re making an app that takes in two numbers and divides them. The pseudocode for that would look a little something like this. First I want to prompt the user to enter a number,
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then I want to wait for the user to input the first number. After I get the first number, I want to again prompt the user to input a second number. Once they do, I complete the operation by dividing the two numbers entered and return the result back to the user. This all seems like it would be common sense, but remember that oftentimes we’re not going to be working with simple multiplication functions, we may be working with full-scale games, algorithms, or user interfaces with many different options. This method allows you the programmer to not get bogged down with the syntax and conventions you have to follow, you’re simply making a note of what the program's ultimate goal should be, as if you were explaining it to a friend of yours. This method really lets you plan out everything that needs to happen in your program in order for it to run smoothly. It also ensures you don’t forget about a piece of an algorithm, or a certain function that you need to write in afterwards. And the final pseudocode strategy that I’d like to talk about today is writing out the main features you want the user to have when using your program, and what functions or
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smaller programs you’re going to need to complete those features. Let’s do another example, say you’re making a banking interface and on start-up, you want the user to initially have 2 different options. They can set up a new account or log into an existing account. From there, if they log into their account you then want them to have the functionality to withdraw money, deposit money, take out a loan, or pay back a loan. If they decide to set up a new account, you want them to be able to create an account, store their information in a database, and then access all of the features that a returning member would have. This may look very similar to the flowchart, the only difference being this is abstracted one level higher, over an entire program rather than just a single function. If you really wanted to, you could also create a flowchart that would go through the functionality of all 4 methods described above. Setting up the hierarchy like seen on your screen now makes it clear to see every function and interface you’re going to have to make. This prevents you from having to try and shoehorn a function or feature into an almost finished
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program at the last second is not a very fun experience in the slightest. So there you have it, 3 pseudocode strategies you can use to plan out your code before you even start writing any. The flowchart method, which is good for thinking through the flow of a certain function. The write-up method, which is good for getting the general idea down for a program, or the functionality planning method, good for listing out the functions of a certain program. You can use none of them, all of them, a mix of them, or even disregard these and find or create your own. The main goal here is to drastically minimize the amount of errors that occur during your programming and relieve a lot of stress on your head. The importance of pseudocode cannot be stressed enough, and if you don’t believe me, I urge you to try and complete a large project without it. Ok, so if you’ve watched the series up until this point, you have gotten a pretty good understanding of many aspects of programming, and also how to plan out your programs. Now it's time to go out into the real world, and write some actual code.
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But what kind of program? I can hear you asking me. And the answer is truly whatever you want, really. As I’m sure you know by now, you can program just about anything that you have on your mind, anything from simple games to complex software. We’ve equipped you with the basics that are going to be used in pretty much any program you do decide to write. But that doesn’t mean every programming language is perfect for every application. Each language has its own strengths and weaknesses, and choosing the right one is very important for making it easier, or sometimes even just possible, for you to program what you want. So that’s what we are going to talk about now: choosing the best language for what you want to accomplish. Now, we talked earlier about low level versus high level programming languages. In case you forgot, let’s do a quick refresher. Higher level programming languages have a high level of abstraction from machine language, that series of 0’s and 1’s from way back when, while lower level programming languages have a low level of abstraction from machine language. For example, block programming where you drag and drop programming statements together
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like 2d legos would be a high level language, as it does not take a high level of understanding of the inner workings of a computer to program it. The theoretical highest level of a programming language would be if I could just write down what I wanted the computer to do in simple english and it would just work. But, sadly, that doesn’t exist yet. On the other side of the spectrum, the lowest level programming language would be just feeding 0’s and 1’s into the computer at supersonic speed, which would be almost impossible and extremely absurd. So, how do you choose what type of language is best for your needs? Well, it depends what you are trying to do, as sometimes you need very specialized languages to get done what you want. The world of computer science is vast and contains many fields, so trying to cover everything in one language would be impossible. This has led to the creation of thousands of different programming languages each designed for a specific task. Right now though, we’ll cover some of the most popular languages and their uses.
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Now, if you are trying to design a website, and delve into that career path, using HTML and CSS is probably your best bet. HTML is a markup language that is designed for writing the content of a website, while CSS is great for designing the style of the website. You interact with HTML code every day and you can even see it right now if you right click and hit inspect element, this will truly show you how complex HTML and CSS can be. Maybe it would be best for you to use a scripting language. A scripting language is a language that has many commands for you to use and that can also be run without needing to be compiled. Scripts can be faster to write than actual programs, and tend to be easier to port between operating systems allowing for cross-platform support. Scripts can also be used with websites, oftentimes adding to the overall user experience of the site. If you want to go into web design, this might also be a path for you to go down. Examples of scripting languages are Perl, PHP, Ajax, and Javascript. If you just want to make a general purpose program, you should probably use a general
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purpose language. General purpose languages, as they sound, have a wide range of applications. Usually these should be your go-to languages. Examples of general purpose languages are Java, C++, and Python. They each have their own different benefits over one another. Java is best at developing games and interactive web pages, Python can act as a scripting language for web programming as well as writing applications and data analysis. And C++ is best for writing applications and system programs. They all have a variety of packages that you can import and use to achieve the functionality you need from them. While selecting the right general purpose language for your big projects is very important, for most of your programs any one of them will work. It really comes down to preference. Get to know each language, and decide which one’s syntax rules you like best and find most comfortable. If you get to know one general purpose language really well and enjoy programming with it, you can apply it to just about any of the programs you plan on writing. Personally, I tend to
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use Python for most of my projects. This is mostly not due to any functional difference between Python and any other general purpose language, though there are a decent amount, but it is mainly because I find its syntax rules most convenient and easiest to write programs with. Overall, either you can consider the project you plan on doing, and research and see which language boasts the most advantages for your purposes, or you can simply become comfortable with a language and use it for most of the projects you decide to write. We’ll now be looking at our final topic of this introduction to programming mini-series. You now have the knowledge of basic programming which will take you far in any language you decide to learn, you know some good pre-programming pseudocode strategies to help you design your code from the ground up, and you might already have a good idea as to the type of programming language you might want to start with, so what’s the next step? How can I learn that language and what applications can it be used for? Well that’s what we’re going to be covering now, so let’s jump right into it.
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Starting with the biggest question which is what’s the next step. Well, now that you might know which type of language you might be interested in, research that language and find out whether or not you truly want to pursue that programming language. Most languages like python or C++ will have either an official website where you can read up on, or a wikipedia page which will provide you with useful information in deciding whether or not you want to pursue that path. From there, the next step is to actually learn the language, which can be done right here on YouTube. While we have taught you the basics of any programming language, each specific language is going to expand upon the basic concepts and so watching tutorial videos on a certain language is going to be very beneficial. Many websites will try to get you to purchase paid courses or take classes which cost money, but you can find extremely good courses here on YouTube for absolutely 0 cost to yourself. I would start with an introduction series like the one you’re currently watching, but for the language you have chosen and work your way through that series, picking up on the syntax and rules of that language until you become comfortable with it. Once you do that, you come to a crossroads. You know how to program in a certain language, but you may be completely clueless as to what to make in that language. Programmer’s block
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can leave you uninspired and not want to continue programming so I’d like to give you a few sites to help out. First is codingbat, a completely free website which has hundreds of coding challenges in Java and Python to help you refine your programming skills and even learn some programming short-cuts and tips. This is great if you want to get better at improving your efficiency and need something to hone your skills as a developer. The next is CoderByte, which offers over 200+ challenges that you can complete in over 10 different languages, something that is sure to help you improve. The final website I’d like to talk about is hackerRank, which not only provides programming challenges to keep you on your toes, but also provides support for using you programming skills to find jobs or internships, something you’ve probably definitely thought about if you are taking programming up as a skill. These and many more websites exist solely to keep you interested in code and work on refining your skills to become better, you just have to find them because they’re certainly out there. Now if you’re a teenager watching this series, I also encourage you to take the programming classes in your high school. AP Computer Science Principles and AP Computer Science A are both
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amazing courses which will help you greatly in the future, and are also incredibly informative and important to colleges. Your school might also offer other classes in the field of computer science, including ones on data structures, game design, and data science. Any and all classes you can take to help expand your knowledge of programming and help you find your niche is going to help tremendously. As you can see, the world of code has now been opened up to you. These are just a few examples of where you can go from here but there are many more we didn’t talk about. You can get into GitHub and start contributing to projects, you can work on your own projects and collaborate with others, the possibilities are endless. The next step is up to you. This concludes our introduction to programming mine-series, we hope you enjoyed watching it as much as we enjoyed making it. If you enjoyed the series as a whole, consider subscribing to our channel NullPointerException, which will be linked in the description, for more content coming soon. Thanks for watching.

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