"Remainder" refers to what's left over after a division, so the remainder of 7/3 (also referred to as REM( 7/3 ) ) would be 1, and the remainder of 7/4 would be 3. The C++ "modulo" operator - % - returns the remainder of the division.

If you're working with bar codes, isn't the last byte already a checksum? I thought that was how they worked....