C++ Primer, Fifth Edition

Using Bitwise Operators

As an example of using the bitwise operators let’s assume a teacher has 30 students in a class. Each week the class is given a pass/fail quiz. We’ll track the results of each quiz using one bit per student to represent the pass or fail grade on a given test. We might represent each quiz in an unsigned integral value:

unsigned long quiz1 = 0; // we'll use this value as a collection of bits

We define quiz1 as an unsigned long. Thus, quiz1 will have at least 32 bits on any machine. We explicitly initialize quiz1 to ensure that the bits start out with well-defined values.

The teacher must be able to set and test individual bits. For example, we’d like to be able to set the bit corresponding to student number 27 to indicate ...