Sometimes a programmer would like one statement, or group of statements to execute only if certain conditions are true. There may be a different statement, or group of statements that are to be executed when the condition is false. An expression that can be evaluated to true or false is called a Boolean expression. (Named after a mathematician named Boole who developed Boolean algebra.)
In C++, the number 0 (zero) is considered to be false, all other numbers are true.
Boolean Expressions: true or false