Why is there a bug?

Hi all, I get an error message when I run this code, can anyone tell me why? Have printed the error messages at the bottom

Code:

---


main()
{
  double x;
  double y;
  scanf("%f", &x);
  scanf("%f", &y);
 
  printf("f(x,y)=%f", f(x, y));
  return 0;
}

double f(double dumx, double dumy)
{
  double result;
 result = (-(3.0*dumy)-(dumx*dumx)+(dumx/3.0)*(1.0/3.0));
return result;
}

---

warning: type mismatch with previous implicit declaration
warning: previous implicit declaration of `f'
warning: `f' was previously implicitly declared to return `int

have you prototyped f() ?

Thanks for the reply, have changed it to this but now when I run it, it will only let me make one input and always returns a value of 0. Does it need a big overhaul?

Code:

---


double f(double dumx, double dumy);

main()
{
  double x;
  double y;
  scanf("%f", &y);
  scanf("&f", &x);
  printf("f(x,y)=%f", f(x, y));
  return 0;
}

double f(double dumx, double dumy)
{
  double result;
 result = (-(3.0*dumy)-(dumx*dumx)+(dumx/3.0)*(1.0/3.0));
return result;
}

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