C++ Primer, Fifth Edition

Writing to a Stream

The first statement in the body of main executes an expression. In C++ an expression yields a result and is composed of one or more operands and (usually) an operator. The expressions in this statement use the output operator (the « operator) to print a message on the standard output:

std::cout << "Enter two numbers:" << std::endl;

The << operator takes two operands: The left-hand operand must be an ostream object; the right-hand operand is a value to print. The operator writes the given value on the given ostream. The result of the output operator is its left-hand operand. That is, the result is the ostream on which we wrote the given value.

Our output statement uses the << operator twice. Because the operator returns its ...