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

int main()
{
  double dt = 0.0001;
  double g = 9.8;
  double vx, vy, x, y, t, ax, ay;
  FILE *f;

  f = fopen("dati.txt", "w");
  if (f == NULL) {
    fprintf(stderr, "Impossibile aprire dati.txt\n");

    return -1;
  }

  vx = 0;
  vy = 0;
  x = 5;
  y = 0;
  t = 0;

  while (t < 10) {
    fprintf(f,"%f %f %f\n", t, x, y);

    x  = x + vx * dt;
    y  = y + vy * dt;
    ay = - g * (x*x)/(x*x + y * y) - (vx * vx + vy * vy) * y / (x * x + y * y);
    ax =   g * (x*y)/(x*x + y * y) - (vx * vx + vy * vy) * x / (x * x + y * y); 
    vy = vy + ay * dt;
    vx = vx + ax * dt;
    t = t + dt;
  }
  fclose(f);	
  return 0;
}