我是c语言的初学者，对程序设计有点疑惑

Question

想问一下这个程序的功能是什么呀，有点看不懂
#include <stdio.h>
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;
}

Answer 1

cumulativeOfsum函数，计算1到n的和
factiorialOfnum函数，计算n的阶乘
sum3=factiorialOfnum(8);
sum4=factiorialOfnum(10);
分别计算8和10的阶乘
sum1=cumulativeOfsum(100);
sum2=cumulativeOfsum(200);
分别计算1到100的总和，以及1到200的总和