C++ Basic Syntax

Lets us begin by simple example of this C++ program, which will print the text "Hello CodingKoleji!" to the screen.

Remember I told you probably the best way to start learning a programming language is by writing a program. Therefore, here is our first program:

The first panel shows above from our online compiler is the source code for our first program. The second one shows the result of the program once compiled and executed. The way to edit and compile a program depends on the compiler you are using. Depending on whether it has a Development Interface or not and on its version. Consult the compilers section and the manual or help included with your compiler if you have doubts on how to compile a C++ console program from our social media support.

Test the above sample code on our online compiler by clicking on the Try it Yourself button.

//my first program in C++
#include <iostream>
using namespace std;
int main(){
  cout<<"Hello CodingKoleji!";
  return 0;
}

The above program is the typical program that programmer apprentices write for the first time, and its result is the printing on screen of the "Hello CodingKoleji" sentence.

It is one of the simplest programs that can be written in C++, but it already contains the fundamental components that every C++ program has. We are going to look line by line at the code we have just written:

// my first program in C++

This is a comment line. All lines beginning with two slash signs (//) are considered comments and do not have any effect on the behavior of the program.

The programmer can use them to include short explanations or observations within the source code itself. In this case, the line is a brief description of what our program is.

We will explain other types of commnets in its section, so don't worry about it.

#include <iostream>

Lines beginning with a hash sign (#) are directives for the preprocessor.

They are not regular code lines with expressions but indications for the compiler's preprocessor.

In this case the directive #include <iostream> tells the preprocessor to include the iostream standard file.

using namespace std; This specific file (iostream) includes the declarations of the basic standard input-output library in C++, and it is included because its functionality is going to be used later in the program.

The header file iostream should be include at the beginning of all programs that use input/output statements.

Here are the list of some of the most common header files in C++ and their purpose:

using namespace std;

All the elements of the standard C++ library are declared within what is called a (namespace)the namespace with the name (std).

So in order to access its functionality we declare with this expression that we will be using these entities.

This line is very frequent in C++ programs that use the standard library, and in fact it will be included in most of the source codes included in these tutorials.

This way we can use the names directly, without having to prepend them with std::. We will see this in action in the next line.

int main ()

This line corresponds to the beginning of the definition of the main function. The main function is the point by where all C++ programs start their execution, independently of its location within the source code.

It does not matter whether there are other functions with other names defined before or after it, the instructions contained within this function's definition will always be the first ones to be executed in any C++ program. For that same reason, it is essential that all C++ programs have a (main) function.

The word (main) is followed in the code by a pair of parentheses (). That is because it is a function declaration: In C++, what differentiates a function declaration from other types of expressions are these parentheses that follow its name.

Optionally, these parentheses may enclose a list of parameters within them.

Right after these parentheses we can find the body of the main function enclosed in braces ({}) What is contained within these braces is what the function does when it is executed.

cout << "Hello CodingKoleji!";

This line is a C++ statement. A statement is a simple or compound expression that can actually produce some effect. In fact, this statement performs the only action that generates a visible effect in our first program.

(cout) represents the standard output stream in C++, and the meaning of the entire statement is to insert a sequence of characters (in this case the (Hello CodingKoleji) sequence of characters) into the standard output stream (which usually is the screen).

(cout) is declared in the (iostream) standard file within the (std)d namespace, so that's why we needed to include that specific file and to declare that we were going to use this specific namespace earlier in our code.

The operator (<<) is called the insertion or put to operator. It inserts (or sends) the contents of the variables on its right to the object on its left, which in this case is the standard output stream. take look at the below image to understand it better.

the object (cout) has a simple interface. If string represents a string variable, then the following statement will display its contents on the screen: (cout << string;).

You may recall that the operator (<<) is the bit-wise left-shift operator and it can still be used for this purpose. This is an example of how one operator can be used for different purpose, depending on the context. This concetp is known as operator overloading, an important aspect of polymorphism in C++.

Operator overloading is discused in details in its section do check

Notice that the statement ends with a semicolon character (;). This character is used to mark the end of the statement and in fact it must be included at the end of all expression statements in all C++ programs (one of the most common syntax errors is indeed to forget to include some semicolon after a statement).

return 0;

The return statement causes the main function to finish. return may be followed by a return code (in our example is followed by the return code 0).

A (return) code of (0) for the main function is generally interpreted as the program worked as expected without any errors during its execution.

This is the most usual way to end a C++ console program.

You may have noticed that not all the lines of this program perform actions when the code is executed. There were lines containing only comments (those beginning by //)).

There were lines with directives for the compiler's preprocessor (those beginning by #)).

Then there were lines that began the declaration of a function (in this case, the main function) and, finally lines with statements (like the insertion into cout).

which were all included within the block delimited by the braces ({}) of the main function.

Structure of the Program

The program has been structured in different lines in order to be more readable, but in C++, we do not have strict rules on how to separate instructions in different lines. For example, instead of

#include <iostream>
using namespace std;
int main(){
  cout<<"Hello CodingKoleji!";
  cout<<"I am Learning C++!";
  return 0;
}

We could have written:

int main(){ cout<<"Hello CodingKoleji!"; cout<<"I am Learning C++!"; return 0;}

All in just one line and this would have had exactly the same meaning as the previous code.

Let us add an additional instruction to our first program:

Example

#include <iostream>
using namespace std;
int main(){
  cout<<"Hello CodingKoleji!";
  cout<<"I am a C++ Programmer";
  return 0;
}

If you run the above program it will produce the two statement in single line.

Now that you have learned the basic syntax of C++ programming. Lets learn how to add more discription to your code by understanding Comment in C++ in the next section.