% is the BASIC operator for modulo arithmetic.
A%B gives the remainder after
A has been divided by
Unlike some implementations of BASIC,
B may be a noninteger. Also,
B may be negative, but the result given is the same as if it were positive. Of course,
B must be nonzero, otherwise the system will generate an error: Division by zero.
A is positive, the result is positive (or zero), and if
A is negative, the result is negative (or zero).