Cos

double cos(double x); 

#include <stdio.h>
#include <math.h>

#define PI 3.14159265

int main ()
{
  double param, result;
  param = 45;
  result = cos (param*PI/180);
  printf ("Cosine of %lf degrees is %lf\n", param, result );
  return 0;
}