fmod() is a Mathematical Function that returns the remainder of x/y. This is same as Modulo Operation.

    float fmod( float x, float y);
    double fmod( double x, double y);
    long double fmod( long double x, long double y);

   #include <stdio.h>
   #include <math.h>
   int main()
     {
        double x = 13.0, y = 2.0, z;
        z = fmod( x,y );
        printf( "The modulus of  %.2f / %.2f is %f\n", x,y, z );
        return 0;
     }

   The modulus of  13.00 / 2.00 is 1.000000

In the above example fmod() function is used to perform modulo operation.