33.求1*2+2*3+3*4+……前n项的和

#include<iostream>
using namespace std;
int XiangCheng(int );

int main()
{
    int n,sum=0;
    cout<<"please input an number : "<<endl;
    cin>>n;
    for(int i=1;i<=n;i++)
    {
        sum+=XiangCheng(i);
    }
    cout<<"the answer is : "<<sum<<endl;
    return 0;
}

int XiangCheng(int index)
{
    int m;
    m=index*(index+1);
    return m;
}