Fermat's little theorem

fermat.c

#include <stdio.h>

int power_mod(int b, int e, int m) {
  int r = 1;
  for (int i = 0; i < e; ++i) {
    r = (r * b) % m;
  }
  return r;
}

int fermat(int a, int p) {
  return power_mod(a, p - 1, p);
}

int main() {
  int a = 8; 
  int p = 11;
  int r = fermat(a, p);
  printf("%d\n", r);
  return 0;
}