red.c

#include <stdio.h>

double red(double x)
{
  int plus = 0;
  int i = 1;

  double sum = 1;
  double last = 0;
  double fact = 1;

  double pot = x;

  do
  {
    last = sum;
    pot *= x;
    fact *= i;

    if (plus)
    {
      sum += pot / fact;
    }
    else
    {
      sum -= pot / fact;
    }

    i++;
    plus = !plus;
  } while (last != sum);

  printf("Broj iteracija: %d\n", i);

  return sum;
}

int main()
{
  double sum = red(4);

  printf("%lf", sum);

  return 0;
}