Figure 10.13  Recursive Function fibonacci
/*
 *  Computes the nth Fibonacci number
 *  Pre: n > 0
 */
int
fibonacci(int n)
{
      int ans;

      if (n == 1  ||  n == 2)
            ans = 1;
      else
            ans = fibonacci(n - 2)  +  fibonacci(n - 1);

      return (ans);
}