最简单的递归形式就是把递归调用置于函数的末尾，即正好在return语句之前，这种形式的递归被称为尾递归 （tail recursion），其形式相当于循环。
/* 递归计算阶乘 */
#include<stdio.h>
long fact(int n);
long rfact(int n);
int main()
{
int num;
printf("this program calculates factorials.\n");
printf("enter a value in the range 0-12(q to quit): \n");
while (scanf("%d", &num) == 1) //输入验证，scanf()函数不读换行符
{
if (num < 0)
printf("no negative numbers, please.\n");
else if (num > 12)
printf("keep intput under 13.\n");
else
{
printf("loop: %d factorial = %ld\n",num,fact(num));
printf("recursion: %d factorial = %ld\n", num, rfact(num));
}
printf("enter a value in the range 0-12 (q to quit):\n");
}
printf("bye.\n");
return 0;
}
long fact(int n) //循环函数
{
long ans;
for (ans = 1; n > 1; n--)
ans *= n;
return ans;
}
long rfact(int n) //递归调用
{
long ans;
if (n > 0)
ans = n*rfact(n - 1);
else
ans = 1;
return ans;
}
