Hello World

The classic first example of a C++ program is the “Hello World” program:

// Look, our first C++ program!

#include <iostream>

int main()
{
  // Print a message to screen
  std::cout << "Hello, World!\n";

  // Return 0 when done
  return 0;
}

If you want to execute it right away, try pasting the code into the online editor+compiler at cpp.sh and hit the “Run” button. As you probably have guessed, this program simply prints

Hello, World!

to screen. (On cpp.sh you get the output in the “execution” window below the editor.)

The program illustrates some C++ basics:

• Comments start with //

• The line #include <iostream> includes standard C++ functionality for input/output. (More about that later.) This enables us to use std::cout in our code. The #include lines in C++ are a bit like the import lines in Python.

• A valid C++ program must have a function called main with return type int (integer):

  int main()
  {
    ...
  }
  

• Program statements end with semicolons (;).

• To write output to screen we use std::cout (pronounced “see-out”).

• Here std:: indicates that cout lives in the standard C++ library. Technically, std is the namespace (more on that later). This is analogous to how the Python code math.sqrt(2) says that sqrt lives in the math package.

• The return keyword ends a function. Since the main function has return type int, we return an integer: return 0; Returning 0 from the main function indicates that the program completed successfully.

So far, so good — next, let’s look at how we can run this program on our own computer.