//  Cout is used to print to the standard output device which
//  is usually a terminal window.

    cout << "Hello world" << endl;

//  Technically endl is a strange beast, but it basically ends
//  up being like using a new-line character.

    cout << "Hello world\n";

//  Using endl will send a new-line and it will force data to be
//  written to the device or file.  Usually '\n' does the same
//  thing but not always.

    cout << "The sum is " << sum << endl;

//  Notice the space in the string before printing the variable
//  sum.  It looks nicer to have a space before a number.