Now here is a puzzle to ponder: Using just the integer operators and

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, determine a set of three assignment statements that exchanges the values stored in two integer variables without using a third temporary variable.

Using the exclusive-or operator to exchange the values of two variables without an extra temp variable is a neat trick, but using a temporary variable is the more common and direct way to accomplish the task.

Are the bitwise operators useful for anything practical? Indeed they are. The power to change a single bit in an integer from 0 to 1 or vice versa, does come in handy. For example, a word processing program may offer you the following five independent formatting features:

With a single mouse click, you can turn each of these features on or off. Of course, a word processing application must keep track of which features are on and which are off. This bookkeeping can be done quite simply by manipulating the bits of a single integer.

Use the five rightmost bits of an integer (or a single byte) to store information about which options (a through e) are turned on. For example:

000 11111 indicates all five properties are turned on; the five rightmost bits are 1.

000 00101 indicates that boldface (a) and underlining (c) are turned on.

000 01000 indicates that subscripting is turned on; fourth bit from the right is 1.

To implement this scheme, declare five final variables:

and another variable to hold the information about which features are on or off.

int format 0 ; // stored as 00000000 indicates that initially all features are off

You can use the exclusive-or operator to change any particular bit of the variable format from 0 to 1 or from 1 to 0 . For example, to store the fact that the boldface and italics features are active, use the statements:

format format ^ BOLDFACE // 00000000 ^ 00000001 00000001

format format ^ ITALICS // 00000001 ^ 00000010 00000011