C++ Hello World

Every C++ program contains one or more functions, one of which must be named main. A function consists of a sequence of statements that perform the work of the function. The operating system executes a program by calling the function named main. That function executes its constituent statements and returns a value to the operating system.

Here is a simple version of main does nothing but return a value:


#include <iostream>
#include <stdlib.h>
int main()
    std::cout<<"Hello world";
    return 0;

The operating system uses the value returned by main to determine whether the program succeeded or failed. A return value of 0 indicates success.
The main function is special in various ways, the most important of which are that the function must exist in every C++ program and it is the (only) function that the operating system explicitly calls.
The main function is required to have a return type of int, which is the type that represents integers. The int type is a built-in type, which means that the type is defined by the language.
The final part of a function definition, the function body, is a block of statements starting with an open curly brace and ending with a close curly.
std::cout<<"Hello world"; getchar(); return 0; }

Semicolons mark the end of most statements in C++. They are easy to overlook, but when forgotten can lead to mysterious compiler error messages.
When the return includes a value such as 0, that value is the return value of the function. The value returned must have the same type as the return type of the function or be a type that can be converted to that type. In the case of main the return type must be int, and the value 0 is an int.

On most systems, the return value from main is a status indicator. A return value of 0 indicates the successful completion of main. Any other return value has a meaning that is defined by the operating system. Usually a nonzero return indicates that an error occurred. Each operating system has its own way of telling the user what main returned.


Hello world