/*  
    file name: fibUsingRecursive.c
    description: Fibonacci numbers
    利用函數遞迴呼叫做費氏數列計算

    費氏數列為0,1,1,2,3,5,8,12,21,…
    其中某一項為前二項之和,且第0項為0,第1項為1
*/

#include <stdio.h>
#include <ctype.h>
#include <stdlib.h>

/* 函數原型宣告 */
long Fibonacci(long);
void flushBuffer(void);

int main()
{
    char ch;
    long n;

    printf("-----Fibonacii numbers Using Recursive-----");
    do {
        printf("\nEnter a number(n >= 0): ");
        scanf("%ld", &n);
        flushBuffer();
        /* n 值大於0 */
        if (n < 0)
            printf("Number must be > 0\n");
        else
            printf("Fibonacci(%ld) = %ld\n", n, Fibonacci(n));
        printf("Contiune(y/n)? ");
        ch = toupper(getchar());
    } while (ch == 'Y');

    return 0;
}

/* 利用遞迴函數呼叫本身函數來計算Fibonacci numbers */
long Fibonacci(long n)
{
    if (n == 0)  /* 第 0 項為 0 */
        return 0;
    else if (n == 1) /* 第 1 項為 1 */
        return 1;
    else  /* 遞迴呼叫函數第 N 項為 n-1 跟 n-2 項之和 */
        return(Fibonacci(n-1) + Fibonacci(n-2));
}

void flushBuffer()
{
    while (getchar() != '\n') {
        continue;
    }
}