Core PHP Programming, Third Edition

3.2. The ? Operator

PHP offers an abbreviated version of the if statement, which borrows syntax from C. It uses the question mark as a ternary operator. Figure 3.2 outlines the format.

Figure 3.2. The ? operator.

conditional expression ? true expression : false expression;

The conditional expression is evaluated to be either true or false. If true, the expression between the question mark and the colon is executed. Otherwise, the expression after the colon is executed. The following code fragment

($clientQueue > 0) ? serveClients() : cleanUp();

does the same thing as

if($clientQueue > 0)
       serveClients();
else
       cleanUp();

The similarity is deceiving. Although the abbreviated form seems to be equivalent to using if-else, at a deeper level ...