4周例5 求阶乘的和

求阶乘的和

描述

给定正整数n，求不大于n的正整数的阶乘的和
（即求1！+2！+3！+····+n！）

mycode

# include <iostream>
# include <cstdio>
# include <math.h>
using namespace std;
int main()
{
//	freopen("C:\\Users\\Lenovo\\Desktop\\algorithm\\test.txt","r",stdin);
	int n,sum=1,fac=1;//阶乘：factorail 
	cin >> n;
	 for(int i=1;i<n;i++)
	 {
	 	
	 	fac*=fac+1;
		sum+=fac; 
	 }
	 cout<<sum;
}