#include <stdio.h>
int main(void)
{
int start;
int end;
long sum=0;
int i,j;
long fac=1;
printf("輸入start和end的值:");
scanf("%d%d",&start,&end);
for(i=start ; i<=end ; i++)
{
for(j=1;j<=i;j++)
fac*=j;
sum+=fac;
}
printf("%d!+...+%d!=%ld",start,end,sum);
return 0;
}
程序只能實現很小范圍的階乘，因為long型的數最大只有 2147483648

#include <iostream>
using namespace std;

long factorial(int n)
{
if(n == 1) return n;
return n*factorial(n - 1);
}

long fun(int *a, int start, int end)
{
long sum = 0;
for(int i = start; i <= end; i++)
{
sum += factorial(a[i - 1]);
}
return sum;
}
void main()
{
int a[5] = {1, 2, 3, 4, 5};
cout<<fun(a, 3, 4)<<endl;
}
30
3*2*1 +4*3*2*1 = 30

int factorial(int num)
{
int i = 0;
int result = 1;
for(int i = 1;i < num+1; i++)
{
result = i * result;
}
return result;
}

int fun(int* a, int start, int end)
{
int result = 0;
for(int i = start; i < end + 1;i++)
{
result = result + factorial(a[i]);
}
return result;
}