Bool Functions

Functions can return bool values just like any other type, which is often convenient for hiding complicated tests inside functions. For example:

The name of this function is isSingleDigit. It is common to give boolean functions names that sound like yes/no questions. The return type is bool, which means that every return statement has to provide a bool expression.

The code itself is straightforward, although it is a bit longer than it needs to be. Remember that the expression x >= 0 && x < 10 has type bool, so there is nothing wrong with returning it directly, and avoiding the if statement altogether:

In main you can call this function in the usual ways:

The first line outputs the value true because 2 is a single-digit number. Unfortunately, when C++ outputs bools, it does not display the words true and false, but rather the integers 1 and 0. (There is a way to fix that using the boolalpha flag, but it is too hideous to mention.)

The second line assigns the value true to bigFlag only if 17 is not a single-digit number.

The most common use of bool functions is inside conditional statements