Test if a number is fibonacci

Question

I know how to make the list of the Fibonacci numbers, but i don\'t know how can i test if a given number belongs to the fibonacci list - one way that comes in mind is genera

Answer 1

int isfib(int n /* number */, int &pos /* position */)
{
   if (n == 1)
   {
      pos=2;  // 1 1
      return 1;
   }
   else if (n == 2)
   {
      pos=3;  // 1 1 2
      return 1;
   }
   else
   {
      int m = n /2;
      int p, q, x, y;
      int t1=0, t2 =0;
      for (int i = m; i < n; i++)
      {
        p = i;
        q = n -p;    // p + q = n
        t1 = isfib(p, x);
        if (t1) t2 = isfib(q, y);
        if (t1 && t2 && x == y +1)
        {
           pos = x+1;
           return 1; //true
        }
      }
      pos = -1;
      return 0; //false
   }
}

How about this?