C++ Programming

C++

    C++ is an up and coming programming language that’s based on objects and compiling. If you’re someone who’s never programmed before, you might be confused by the words object and compiling. A program that utilized compiling is read by the computer’s CPU rather than by being interpreted by a program installed on the computer to run that program. Therefore, the program speaks more to the computer’s processing system rather than a program.  You may already know this, but computers are not able to read letters and have to read binary code, so the code has to be translated into a computer readable one. This process is known as compiling. Now, object-oriented code is just how the code is structured. You’ll understand that tidbit a little better in the following chapters.

    So what does that all mean and why do you need to know it? As a programmer using C++, you’re going to need more than just the average text editor. There only a few programming languages where that’s all you’ll need, and they’re not really programming languages. One of the things you are going to need is a compiler. Another thing you’re going to want is an Integrated Development Environment, also known as an IDE. This is a programmer-oriented text editor that has a syntax highlighting and is compiler integrated. For Windows and Linux, you can use a few different options.

    You don’t really need an IDE because a basic text editor will do, but something like Notepad is going to make things a little more difficult. Word processors are also a bad choice because they have autocorrect with spelling and grammar, which will mess up your code if you’re not careful.

    To begin with C++, you should understand that it has a rigid syntax. This means the code is case sensitive, so typing ‘Hello’ is going to be different than typing ‘hello’. In addition, you should know that the programming language doesn’t care much about white space, so don’t worry about it. So that’s about all you need to know about C++ when you first begin. Let’s get  into some actual coding to get you started!.

Your First Program

    Due to this being a short tutorial on how to get started with C++, we’re going to start you out with a program in the first chapter. Your first program is going to be very simple. All you’re going to do is write a single phrase on the screen, but it’s not as simple as writing it in a Word document. First, let’s take a look at the code and then we’ll go further into what it means. The line is going to tell the compiler it has to link to the iso stream library to the program. A library is a repository where snippets of code are stored, known as functions. The library also stores other things, like variables and sometimes operators.  The isostream library has code that will let you send characters into the text stream, which is then fed onto the screen. Think of it like a river. You’re the river’s source and the screen is the sea. Whatever is put into the river from the source is going to go onto the screen.

The following line, line two, lets the compiler known that you want to use the namespace known as std, which is a standard namespace. Namespaces are an area where the code is stored. This is useful if you have two pieces of code that have the same name. Normally, pieces of code are not able to share the same name, but if one of is in a separate namespace than the other, then they can have the same name.

The third line of code is the beginning of the code. It’s the main block, as the name implies. Everything inside the braces {} will be translated by the compiler. You’ll need that line in every program because nothing will happen without it.
Now comes the printing of the phrase, ‘Hello World!’ To do this, you use code that’s stored inside the isostream library. This part of the code is known as the statement or cout, which sends information to the stream. The << that comes after the coutis an operator. This means ‘output’, so with the coutit all translates to ‘output this stream’.

The following stream is ‘Hello, World!’ and is known as a string. Strings are a sequence of characters and are shown by enclosing them in double quotation marks. This ends with a semicolon and signifies the end of the statement. If the semicolon is not used, then the program is not going to compile.

The last line, not the closing brace, is very simple but also very important. It’s placed at the end of main and tells the computer that the main block has been finished. It will return a value of 0 to the CPU. A non-zero value will create an error, so it’s a necessary line.

Now that you have the source code of the program, you have to compile i. If the program closes once you run it, then try running it from the cmd/terminal prompt instead. Now that you know how to create your first program and what it looks like let’s take a look at variables!

Variables

In the last chapter, variables were mentioned and it was said that they would be discussed. Now is the time to discuss them. A variable is something that stores a value. Imagine that every variable is a box and every box is labeled with a name and category.

The category is what type of item it’s storing and its name is the specific variable it’s called. Boxes are able to store many things, but only if that thing fits inside the box. This is the same with variables. They all have a type, name, and size that govern what they are and are not able to store.

For example, one type of variable is the integer. If you know basic mathematics, then you know that integers are zero, whole numbers, and their negative counterparts. So -5, 4, 0 and -378 are all integers. In addition, integer variables will have a fixed size.

They are only able to hold one number between two others. These are specific to the variable and will not be discussed quite yet, but a default integers range is between -231 = -2, 147, 483, 648 and 231– 1 = 2, 147, 483, 647. You probably won’t need numbers larger than that yet, so we’ll save the rest for another time.
Here’s a table to see the different types of variables you can use.

There are a few different variable types. You’ll probably use them all when you program, but for now you’re only going to use a few.

Using Variables

Take a look at the following program:

Most of this program is going to look familiar, except for the fourth and sixth lines. The first unfamiliar part declares the variable. This is telling the compiler that you’re going to use a variable. In declarations, the variable type is going to come first. In the example, it's using the int type. Next is the variable’s name, which would be known as var.

It’s easy and simple. A variable name can be anything, but be sure it’s something relevant and not something that’s already reserved and means something in C++ and it doesn’t begin with a number or a special character. You should start with a lowercase letter, and end the statement with a semi-colon.

Line nine in the code above is known as an assignment and assigns a value to the variable. The equal sign is the assignment operator, and it is what does the assigning. The variable on the left is given the value on the right, and the = is a binary operator because it has two operands. One to the left and the other to the right. The operand on the right doesn’t have to be a value. It can be another variable. The left has to be a variable and you can’t change the meaning of the number seven. In the example, the integer variable var is a value of forty-two.
You can see the cout statement doesn’t have quotations marks around the variable name. That’s because you want to output the value of the var and not display the string ‘var’. If you were compiling the program, it would print ‘42’ because that is the value the var has. Try changing it to another integer and look at the output.

Variables also have prefixes that are added to their declaration that changes how they act. Some will change the size, and others will not allow negative numbers, and others might do something entirely different.

Now that you know about variables let’s talk about how to expand the program!

Expanding Your Program

Now that you know how to use variables and how to put them into the program let’s take a look at how to expand the program. All you really know what to do is use the variables and put them into your program, so all you can really do is set the output and values of the variable. That isn’t useful when you’re creating a real program.

What you need is a way to manipulate the variables and receive input from a user. So let’s take a look at the next!

iostream Library

You already know that the iostream library is able to output data, but it can also obtain input data, too. The command is very like the cout statement. The command is cin. There is one different, though. When you use cin, the operator after it’s inverted.

Instead of being <<, it’s >>. This is confusing to remember in the beginning, but you’ll learn it eventually. Note that when you run the program, you’ll need to press the enter key after you put in the desired information, like a terminal/cmd prompt.

Take a look at the following program to see the difference between the two.

Now you can probably see that it’s simple to get the user’s input using the iostream library, which produces some more useful programs. iostream is a lot more powerful, though. You can combine many statements into one.

For example, to put out two strings or variables you would normally need two statements, but you can combine many cout statements and produce a much shorter code. All you have to do is just add another operator for the item you’re outputting or inputting.

For example:

You can also combine together cinstatements in the same way you’d receive several parts of the input in a row. Enter has to be pressed after each one, and you can’t mix input and output on a line of code.

Now that you know how to combine code and expand your program let’s talk more about operators.

Operators

You’ve learned how to output text, declare a variable and obtain input, but you can’t do anything with the variables. Sure, you can give them values, but what use is that in the real world? What you really need is a way to manipulate the variables without doing hard work. Luckily, the operators will save you!
You’ve already investigated two operators that are linked to the iostream library, the input and output or >> and <<.

These operators are able to be put into categorical groups, the first one being arithmetic operators. These are -, +, /, and *. You would use them exactly you would use them in math. For example, this piece of code will add two numbers together and display the results.
 

Now that you know how to use operators let’s take a look at conditionals!
 

Conditionals

It’s great to have a program that does single, linear tasks, like saying ‘Hello’, but it’s rare that you’re going to come across for the need of having a program that does linear tasks only. Programs usually use something known as conditions, or statements that can branch the code into different paths depending on whether a condition is true or not. It’s like a fork on the road, basically.

C++ conditionals have the form of if statements. For example, if something is true, execute this line of code, if something is false, execute another line of code. Take a look at the following code piece as an example.

Lines one through five should be pretty obvious to you by this point, but line three is the one where you may need a little explanation. This is the example of the if statement. It operates by first taking the matter of the integer variable a, and checks to see if it’s less than 2. If that’s true, then it’ll run the code that’s in the curly brackets.
If it’s not, then it will continue as if the piece of code didn’t exist. We know that

1 or the value of a is less than 2, so if you were to run this program, then you’d see ‘a is less than 2!’ on the screen.

Here there is another operator introduced, the less than one, <. If you’re familiar with math, then the use of this sign is pretty self-explanatory. If you’re not, then you’ll need to learn it. Note that while < looks like <<, they are not even close to the same thing and are not related in programming.
Of course, C++ is a strong language, and so it’s able to do more powerful things using these condition if statements.

So in summary, C++ conditionals start with an if statement, and they can have a number of else ifs after them, too. An important thing you should remember is that once one of them has been satisfied, then all the rest is going to be skipped. If you want all of your if statements checked, then do several single if statements one after another.

 

Loops

Now you’re able to write code that is able to read input from the user, do different things depending on the input, and then show the results, but if what if you want to do the same thing but with some different parameters, several times? It would be boring to write the same code over and over again, and awkward if you don’t know how many times you need to run that piece of code when you’re writing it. What if it depends on something the user entered?
To complete this action, you’ll need to use something known as a loop. Loops are a piece of code that are repeated several times, one after another until a condition is met. C++ has three different types of loops. There’s the while loop, the for loop and the do while loop. Let’s start with the while loop since it’s the easiest.

While loops look like if statements, almost.

The use of ‘while’ is evident when you know what while loops actually do. Here, the code is saying that ‘while the value of in the userInput variable does not equal 10, obtain some input from the user’. In addition, remember the ! means ‘not’ in C++, so the code ‘!=’ translates to not equal.

If the userInput is ten, then the code is not going to be executed and the loop will be skipped. While loops can be seen as being an if statement that jumps back to the information in itself once the code has been run.
Before we keep going, it’s important to know that the following piece of code is
usable in C++:

It actually has its own name. It’s an infinite loop so it will loop infinitely. Going through the code, you’d get something like ‘Is 1 equal to 1? Yes it is, print an ‘a’.’ This will repeat over and over again. There are other ways to make infinite loops, but you probably don’t want to make one.

The second type of loop is the do while loop. Do while loops look like this:

While it looks different than the standard while loop you just saw, it’s almost the same thing, except there’s one difference. The while loop evaluates a condition to see if it’s true and will run the code if it is, and the do while loop will execute some code and then check to see if the condition is true. Due to this happening, no matter what you initialized as userInput to the code between the curly- brackets will definitely run.

The third type of loop is the for loop. This is the more complicated out of the three, but it’s powerful when you understand it. For now, let’s just cover the uses. Take a look at this for loop.

This piece of code tells the program to start by setting the value i to 2 and as long as i is less than 10, then output its value to the screen and increment. You can easily replicate this loop using a while loop, but it uses a lot more line of code and is pretty untidy.

You should also know that the variables used in the first line of the for loop have to be the same variable. You also should remember that the first statement is not a conditional, it’s an assignment.

This kind of loop comes in handy when you want to step through various pieces of data, and you’ll see this when you read about arrays in the next chapter. 

Arrays

Arrays are a list of variables that are grouped together because they have a common use. They don’t really have to have something in common, but when you put unrelated things together it’s not really a good idea. It’s like filling your filing cabinet with random papers and never organizing them. What the need for a filing cabinet of you’re going to do that?
Here’s a declaration of an array of integer variables.

1 int a [5];

You can see that arrays look like normal variables, but they have some square brackets at the ends. When you declare arrays, the brackets are then filled with the size of the array you’re looking for. In this case, you’re going to store five integer variables.

An array can be whatever size you want as long as you have the RAM to spare, but it can hold only one type of variable at once. The variable type can be something you’d normally use.

Accessing a certain variable in the array is simplistic. You put the numbers of variables you want in the square brackets. So for the first variable you want [0], for the second you put [1] and keep going. Take a look at the following example.

One thing you shouldn’t do is access a variable that’s not in the array that doesn’t exist, like the tenth variable in an array that has five places, or doesn’t have a variable assigned to it. If it doesn’t have a variable assigned to it, you’ll get what’s known as a garbage value because the value it returns is not going to be useable.

If the variable doesn’t exist, you can get a segmentation fault because the program will try to access a segment of memory that it’s not allowed to. This can result in the program terminating unexpectedly.

Now that you know how to create arrays let’s take a look at creating functions!

Functions

Functions are a great way of writing out complex programs without needing to repeat code. For example, let’s say you have a complicated part of code that gets some input from the user and parses it. Now let’s say you need to run the code several times, but not in a loop. Up until this point, you’d have to write it out every time.
With modern copying and pasting, it’s not that big of a deal, but it’ll look horrible and having repeated code can be a problem when you go to fix any errors. To remedy this problem, you can create functions, which are pieces of code that you’re able to call repeatedly without needing to write it out every time.

Actually, you’ve already used a function. Main is a function. So let’s take a look at it to see how it works.

Let’s examine the first line, the one that has the word main in it. This begins the definition of the function that will take no parameters, known as main, and will give back a value of type int. You already known what an int is, a type of variable, but what does return a value mean?

A function in C++ is like a function in math, you insert a number and some operation is performed on it, and you get an answer. Here, the int is the variable that the output function is going to be. A parameter is the variable that is put into the function, and then the function performs an operation before it returns the results.

Let’s take a look at a function that has a main.

The parameters are written like a variable definition and is separated by a comma. They are written right after the function name and are closed in by parenthesis. Now there is an integer value known as argc and an array of characters known as argv as the parameter. You can use any type of variable you want as a function parameter, as long as when you use that function you provide a variable that’s of the same type.

Now that you know what a function is and does let’s take a look at pointers.

Pointers

RAM or random access memory is where the computer saves all the variables the program uses, and is basically a long line of numbers. Every number is identified by the address or where it is on that line. These are logical, so the number with the address four comes after the three but before the five.
The exact size of the number at that address is figured out by the computer architecture. Say you have two integers and a character. One might have an address of 1000 while the other has an address of 1004. The character or char might have an address of 1008. So why is there a four byte gap between the variables? Integers are four bytes long, and so they take up four addresses in order to store their value. It doesn’t matter if you use one byte and don’t use the other three, it will still take up four bytes of memory.

But why do you need to know this? C++ programmers need to know that their compiler does not have fancy addressing for them, translating their variables into addresses in RAM, but sometimes it’s good to know the translations on our own. Think about how the arrays work for a moment, they are just long lines of variables whose type is what the programmer tells the compiler.

So you might be thinking this is just like RAM and you’d be right. When you labeled the arrays and the fifth value was actually the number six because all arrays start at zero, you’re actually taking the fifth variable after the first variable. So if you say the array is an integer one, with the first integer coming from RAM address 1000, then combine that will what you know about integers being in four bytes, you can see that the nth integer in the array would have this
address:

Therefore, the address of the sixth element is 1020. So why is this useful? You can make the array while the program is compiling and running and make it the proper size.

A pointer is a normal variable, but instead of storing the integer, it stores the address of another variable. Here is a pointer.

In this pointer, you have a variable that stores the address of the integer. The * is the variable as a pointe rand not a normal variable. You’ve assigned it to the value of zero. When you assign values to pointers, you’re not giving them numbers or characters, you’re giving them the address of another variable.
Now that you know what they are, let’s move on to dynamic memory in the following chapter.

Dynamic Memory

So far you’ve been able to create variables at compile-time and modify them during run-time; however, you can create them in run-time, too when you use dynamic memory allocation. This method uses allocation and deallocation of RAM as the program is running. Since you’re accessing RAM, it’s natural to assume that you’ll do it with pointers, but dynamic memory in C++ is utilized differently than it is in C.

Take a look at the following block of code.

Here you’ve made a pointer to an int and set aside some memory for it. Since i is still the pointer, not a variable, you’ll have to set the value pointed to by i to five and not i. This changes the location point by i and orphaned the set aside memory in RAM somewhere. This memory that’s been forgotten is known as memory leak. To stop this, be sure to deallocate the memory you set aside in the first place using the delete operator.
Allocating memory down to single variables doesn’t help much, though. If you know the variable was going to exist then you could declare it normally. What this does is create variable size arrays that are not known as compile-time. How would you possibly know it, really? You can’t create an array of pointers and tap into them as you need them, that’s just a more RAM intensive version of making gigantic array and hoping everything goes well.

Now that you know what dynamic memory is and how to use it let’s take a look at classes and objects in the following chapter.

Classes and Objects

This is actually what C++ was made to do, support classes and objects. Without them, C++ is just really C. But what are the classes and objects that have been mentioned before? Classes are like a type of mold and the object is the thing that comes from the mold. These molds are flexible and are able to be used to make whatever type of object you’d like. The molds can be general or they can be specific.


So let’s say you want to make a vehicle. This is going to be an abstract tutorial as the code is not actually doing to do anything. Think of what properties a car needs. They need speed, price, color, manufacturer, and a model. What about if it’s four wheel drive or not? And what can you do with it? Can you start the engine and stop?

Let’s take a look at the class definition of what the car looks like.

So as you can see, classes are defined a lot like structs, and that makes sense because they are both a way to group data. But this class contains something that a struct is not able to, functions.

Conclusion

So by now you know how to create your first, simple program and much more! You know what a variable is, how to expand your program, how to use operators, conditions, loops, arrays, functions, pointers, dynamic memory, and classes and objects to morph your program into a masterpiece! You see, C++ was not as difficult as you may have once though it was.

The next step is to gather the knowledge you’ve gleaned from this book and go on to read more about the wonderful world of C++ programming. Once you’re comfortable, set up a virtual machine to do your coding in and get started! You’ll learn a skill that’s highly valuable in the computer industry today.

Thank you for reading. I hope you enjoy it. I ask you to leave your honest feedback.