Your first program

Learn to write your first C++ program with main, #include and iostream.

Your first program

The entry point of every C++ program is the main function. When the program starts, main is called and runs until return 0;.

To write a program you first include the standard I/O library with #include <iostream>. std::cout prints text to the screen; std::endl ends the line and moves the cursor to the next line.

From the command line you compile with g++ hello.cpp -o hello and run with ./hello. C++ source files usually use the .cpp extension.

What is #include?

#include is a preprocessor directive: before compiling, the compiler pastes the named header file into your source. <iostream> provides std::cout and std::cin for input and output.

Header names go inside <...> and are not followed by a semicolon. Standard library headers do not use a .h extension; for your own headers you write #include "mine.hpp" with quotes.

A program can have several #include lines; each one must be on its own line.

Exercise Write your first program

Complete the skeleton below. Inside main, use std::cout to print Hello World and end the line with std::endl.

Show example solution

#include <iostream>

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

Test yourself

What is the entry point of a C++ program?
- the start function
- the main function
- the run function
- the init function
Show answer

the main function — The main function is the entry point of a C++ program.

The #include line

#include <____> to include the input/output library.

Show answer

#include <iostream> to include the input/output library.

Match the program parts

int main()

Entry point
return 0;

Successful exit
std::cout

Output writing
#include

Library inclusion

Next lesson: std::cout

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