Logical OR (||) Operator

Now let’s consider the || (logical OR) operator. Suppose we wish to ensure that either or both of two conditions are true before we choose a certain path of execution. In this case, we use the || operator, as in the following program segment:

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which contains two simple conditions. The simple condition semesterAverage >= 90 evaluates to determine whether the student deserves an “A” in the course because of a solid performance throughout the semester. The simple condition finalExam >= 90 evaluates to determine whether the student deserves an “A” in the course because of an outstanding performance on the final exam. The if statement then considers the combined condition

and awards the student an “A” if either or both of the simple conditions are true. The message “Student grade is A” prints unless both of the simple conditions are false. Figure 5.16 is a truth table for the logical OR operator (||).

Fig. 5.16. || (logical OR) operator truth table.

The && operator has a higher precedence than the || operator. Both operators associate from left to right. An expression containing && or || operators evaluates only until the truth or falsehood of the expression is known. Thus, evaluation of the expression

stops immediately if gender is not equal to FEMALE (i.e., the entire expression is false) and continues if gender is equal to FEMALE (i.e., the entire expression could still be true if the condition age >= 65 is true). This performance feature for the evaluation of logical AND and logical OR expressions is called short-circuit evaluation.