This simple program above, just displays a message "Hello world" (what else!) on the display.

 

Let us try to analyze various parts of this program now.

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main() function

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All C++ programs must have a function called main(). main function is the starting point of execution of the program.

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int main()

 

Some of you might ask me - why is it int main()? Shouldn't it be void main()?

 

The answer is - Every  function has a return type. And the return type is specified in the function header before the function name. This return type is  the type of the value it returns.

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e.g.

int product(), double findAver() etc.

 

If the function does not return a value, its return type is specified as void.

 

As we told already, the type of the return value is specified before the function name in the function header.

 

In this case , main() function returns an integer value.

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We will see this concept in detail later when we talk about functions.

 

Note: main() function can also take optional arguments called command line arguments and optional environment arguments.

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cout object

 

In C++, the input and output operations are performed using two objects viz cin and cout (console in and console out) which are instances of input stream and output stream.

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cout is the object used to display values on console. It is an object of ostream class and it uses the overloaded operator << (insertion operator).

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e.g.

cout<<10; 

cout<<m<<n;

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The first line prints 10 on the screen. And second line prints the values of variables m and n.

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endl

 

endl is a constant which stands for '\n' (new line) character. It displays a newline character. This endl  takes cursor to the next line.

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namespace std

 

As  C++ programs get really complicated, related code and classes are placed in different groups called namespaces. To use classes, objects etc. from a namespace, you should import that namespace into your program. That is done by using statement.

 

All the standard library objects are available in a namespace called std.

 

That is why you need to import the namespace std into your programs with the line

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     using namespace std;

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iostream or iostream.h?

 

If you are familiar with C language, you might have used, include statements with .h (header files) extensions and will be tempted to add   .h to your include filenames.

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In modern C++ compilers, cin, cout, endl and other i/o classes and variables are declared in a file called iostream - without .h extension. That is the reason we need to include this header  file iostream.

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Some older compilers may still use iostream.h. But most compilers use the header files without .h extension.

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Compiling the program

 

A compiler is a software which converts your program written (in C++ here) in high level language into machine language - a language your computer can understand.

 

There are many C++ compilers available - most of them are free. The preferred one is always gnu compiler g++. Using g++, you can compile the program as follows.

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                 g++ myprogram.cpp

 

Here is a guide on how to use g++

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Like C program, the C++ compiler creates an executable file with the name a.out (in a Linux system) and file with extension .exe in windows system. You can execute this by exeuting a.out.

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You can also use C++ integrated development environments like eclipse, VisualStudio, codeblocks, QtCreator etc to develop your programs.

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Now go ahead and type and run your hello world program in C++.