/* fib4.c -- Fibonacci-Zahlen, iterativ (konstanter Platz), unsigned short */

#include <stdio.h>

unsigned short fibonacci (unsigned short n)
{
  if (n == 0) return 0;
  else if (n == 1) return 1;
  else {
    unsigned short a = 0;
    unsigned short b = 1;
    unsigned short i = 2;
    while (i <= n) {
      /* Invariante: a == F(i-2) und b == F(i-1) */
      unsigned short sum = a + b;
      a = b;
      b = sum;
      i = i + 1;
      /* Wieder korrekt */
    }
    /* Hier ist i == n + 1, also b == F(n) */
    return b;
  }
}

int main ()
{
  unsigned short n = 0;

  while (n <= 50) {
    printf("F(%u) = %u\n", n, fibonacci(n));
    n = n + 1;
  }
  
  return 0;
}