C语言网题目 1013: [编程入门]Sn的公式求和

#include<iostream>
using namespace std;
int main()
{
    int n;
    cin >> n;
    int sum = 0,num = 0;
	for(int i = 0 ; i < n;i ++)
	{
		num = num * 10 + 2;
		sum += num;
	 } 
    cout << sum;
    return 0;
}