This page introduces how the "mod" % operator works in Java and other languages along with a few live practice code problems.

Mod % Operator

Modulus operator % -- "mod" for short

e.g. 23 % 10 → 3

Repeatedly subtract 10 from 23 .. what's left?

Like the "remainder" after dividing by 10

Basically all languages use the % symbol for mod

You're familiar with the 4 arithmetic operations + - * /. The % modulus operator is an additional arithmetic operation: basically the remainder left over after division. For example, what is 73 % 10? The simplest way to think about it is, keep subtracting 10's from 73 until there's less than 10 left (3 in this case).

Mod yields 0 means divides evenly

e.g. 30 % 10 → 0

"N multiple of 5?" → (N % 5) == 0?

Key Features of Mod

When mod by N yields 0, N divides in evenly

Mod by N yields a number in the range 0..N-1 (inclusive)

e.g. mod by 10 yields 0..9

e.g. mod by 100 yields 0..99

Don't mod by 0, it's an error (like divide by 0 is an error)