#include <string.h>

int strcmp(const char * s1, const char * s2) {
  size_t i = 0;
  while(s1[i] != '\0' && s2[i] != '\0') {
    if(s1[i] != s2[i]) {
      return s1[i] - s2[i];
    }
    i++;
  }
  return s1[i] - s2[i];
}