#36 ANATOMY OF A C++ PROGRAM

C++ programs are organised into classes comprising of member functions and member variables. A simple HelloWorld.cpp like below can be classified into two parts: the preprocessor directives which start with # and the main program that starts with int main()

#include <iostream>

int main()
{
    std::cout << "Hello World" << std::endl;
    return 0;
}

A preprocessor is a tool that runs before the actual compilation starts. Preprocessor directives are commands to the preprocessor that always start with the # symbol. A custom header created by the programmer will be encapsulated by quotes "..." instead of brackets <...> which are typically used when including standard headers.

Custom: #include "...relative path to file\file.h"

Typical: #include <file.h>

After the preprocessor directive(s) is the body of the program characterized by the function main(). It’s a standard convention that function main() is declared with an int preceding it. int is the return value type.

Functions in C++ need to return a value unless specifically specified otherwise. In main() an int is always returned since it is indeed a function. This is very useful since it provides the ability to query on the returned value of the application. A typical success return value is 0 and in the event of an error -1 is returned.

Namespaces are names given to parts of code in order to reduce naming conflicts. By invoking std::cout, you are telling the compiler to use that one unique cout that is available in the std namespace.

C++ has two comment styles:

// indicates the start of a line and is valid to the end of that line.

/* followed by */ indicates the contained text is a comment.

Functions enable you to divide the content of your application into functional units that can be invoked in a sequence of your choosing. In a C++ console application main() is the starting function of your application.

Example of using functions in C++:

#include <iostream>
using namespace std;

//Declare the functions
int Demo_1();
int Demo_2();

int main()
{
    Demo();
    Print();
    return 0;
}

int Demo_1()
{
    //subtraction
    int x = 8;
    int y = 6;
    cout << x-y << endl;
    return 0;
}

int Demo_2()
{
    //addition
    int x = 8;
    int y = 6;
    cout << x+y << endl;
    return 0;
}