C Primer Plus®, Third Edition

The Conditional Operator: ?

C offers a shorthand way to express one form of the if else statement. It is called a conditional expression and uses the ?: conditional operator. This is a two-part operator that has three operands. Here is an example that yields the absolute value of a number:

x = (y < 0) ? -y : y;

Everything between the = and the semicolon is the conditional expression. The meaning of the statement is this: If y is less than zero, then x = -y; otherwise, x = y. In if else terms, the meaning can be expressed as follows:

if (y < 0)
    x = -y;
else
    x = y;

This is the general form of the conditional expression:

					expression1 ? expression2 : expression3
				

If expression1 is true (nonzero), then the whole conditional expression has ...