分析上例两个实例，解释程序的具体功能。

#include
int fib(int n);
int main(void) {
int n;
printf("输入斐波纳契数列的下标: ");
scanf("%d", &n);
printf("斐波纳契数列第%d项的值: %d\n", n, fib(n));
return 0;
}
int fib(int n) {
if(n == 0 || n == 1)
return n;
else
return fib(n - 1) + fib(n - 2);
}

#include
int cumulativeOfsum(int n);
int factiorialOfnum(int n);
int main()
{
int sum1,sum2;
long int sum3,sum4;
sum1=cumulativeOfsum(100);
sum2=cumulativeOfsum(200);
printf("1到100的累加和是：%d\n",sum1);
printf("1到200的累加和是：%d\n",sum2);
sum3=factiorialOfnum(8);
sum4=factiorialOfnum(10);
printf("8的阶乘是：%d\n",sum3);
printf("10的阶乘是：%d\n",sum4);
}
int cumulativeOfsum(int n)
{
int i,sum;
sum=0;
for (i=1;i<=n;i++)
{
sum=sum+i;
}
return sum;
}
int factiorialOfnum(int n)
{
int i,sum;
sum=1;
for (i=1;i<=n;i++)
{
sum=sum*i;
}
return sum;
}