double modf(double , double *int);

Splits completely paid off and returns the fractional part of x.

compile in linux with: gcc modf.c -o modf -lm -Wall

#include <stdio.h> /* including standard library */
//#include <windows.h> /* uncomment this for Windows */
 
#include <math.h> /* including math library */
 
int main ( void )
{
  double i, result;
  result=modf(4.2, &i);
  printf ("%lf + %lf = %lf \n", i, result, 4.2 );
  return 0;
}

  output: ./modf 
  4.000000 + 0.200000 = 4.200000