C++ Primer, Fifth Edition

Using a Conditional Operator in an Output Expression

The conditional operator has fairly low precedence. When we embed a conditional expression in a larger expression, we usually must parenthesize the conditional subexpression. For example, we often use the conditional operator to print one or another value, depending on the result of a condition. An incompletely parenthesized conditional operator in an output expression can have surprising results:

cout << ((grade < 60) ?   "fail" : "pass"); // prints pass or  failcout << (grade < 60) ?   "fail" : "pass";   // prints 1 or 0!cout << grade < 60 ?   "fail" : "pass"; //  error: compares cout to 60

The second expression uses the comparison between grade and 60 as the operand to the << operator. The ...