// 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.