From Math Operators and Functions on the wiki: % , for modulus division. The result of a % b is the remainder of a / b . If you think back to when you were first learning long division without getting into decimals, you were learning how to perform modulus division. Modulus is useful, for example, to test whether a value is even or odd: a % 2 will be 0 if a is even (and positive) and 1 if a is odd (and positive). In general, the result of a % b when a and b are both whole numbers will be a whole number in the range [0, |b| - 1] where |b| is the absolute value of b. (If a is less than 0, the result will be negative, including -0. -0 is functionally equivalent to 0.)
