/*
 * Program demonstrating use of recursion to compute Fibonacci
 * numbers.  (This is actually an incredibly inefficient way to
 * compute them, but pretty, and a good example of recursion.)
 *
 * Input:  a non-negative integer n.
 *
 * Output:  the n-th Fibonacci number.
 */
#include <stdio.h>

/* Compute n-th fibonacci number and return it */
int fib(int n) {
	/* base case -- 0th and 1st numbers are 1 */
	if (n <= 1) {
		return 1;
	}
	/* for n > 1, n-th number is sum of previous two */
	else {
		return fib(n-1) + fib(n-2);
	}
}

/* Main program */
int main(void) {

	int n;
	printf("enter a non-negative integer\n");
	if (scanf("%d", &n) != 1) {
		printf("error:  not an integer\n");
	}
	else if (n < 0) {
		printf("error:  negative\n");
	}
	else {
		printf("the %d-th Fibonacci number is %d\n", n, fib(n));
	}
	return 0;
}