5.6. Boolean Variables

As usual, for every type of value, there is a corresponding type of variable. In C++ the boolean type is called bool. Boolean variables work just like the other types:

bool fred;
fred = true;
bool testResult = false;

The first line is a simple variable declaration; the second line is an assignment, and the third line is a combination of a declaration and as assignment, called an initialization.

As I mentioned, the result of a comparison operator is a boolean, so you can store it in a bool variable

bool evenFlag = (n % 2 == 0);     // true if n is even
bool plusFlag = (x > 0);    // true if x is positive

and then use it as part of a conditional statement later

if (evenFlag) {
  cout << "n was even when I checked it";

A variable used in this way is called a flag, since it flags the presence or absence of some condition.

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