floor

fdim

#include <math.h>float fdimf(float a, float b);double fdim(double a, double b); long double fdiml(long double a, long double b);

fdim( ), fdimf( ), and fdiml( ) were defined by C99.

The fdim( ) family of functions returns zero if a is less than or equal to b. Otherwise, the result of a – b is returned.

Related functions are remainder( ) and remquo( ).