#include <stdio.h>
#include <math.h>
/* #define NDEBUG 1 */       /* if NDBUG is defined, the assert facility is disabled */
#include <assert.h>

int isSmallNumber(double x){
  return (fabs(x) < 0.0000001);
}   

double my_sqrt(double x){
  double res;
  assert(x >= 0);   /* PRECONDITION */
  res = x / 2;
  assert(isSmallNumber(res*res - x));   /* POSTCONDITION */
  return res;
}

int main(void) {

  printf("my_sqrt(15.0): %lf\n", my_sqrt(15.0));
  printf("my_sqrt(20.0): %lf\n", my_sqrt(20.0));
  printf("my_sqrt(2.0): %lf\n", my_sqrt(2.0));
  printf("my_sqrt(16.0): %lf\n", my_sqrt(16.0));
  printf("my_sqrt(-3.0): %lf\n", my_sqrt(-3.0));
  
  return 0;
}