The C++Course provides a general introduction to programming in C++. It is based on A.B. Downey's book, How to Think Like a Computer Scientist. Click here for details.

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 positiveFlag = (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" << endl;

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

Last Update: 2005-12-05