5-38 数列求和-加强版 (20分)

#include<iostream>

using namespace std;

int main(void)
{ 
	int A, N,flag,temp;
	long j=0;
	int *num;
	cin >> A >> N;
	if (N == 0)
	{
		cout << N;
	}
	else
	{
		num = new int[N];
		flag = 0;
		for (int i = N; i >= 1; i--)
		{
			temp = A*i + flag;
			flag = temp / 10;
			num[j] = temp % 10;
			j++;
		}
		if (flag > 0)
		{
			num[j] = flag;
		}
		else
		{
			j--;
		}
		for (int i = j; i >= 0; i--)
		{
			cout << num[i];
		}
		delete[] num;
	}
	
	return 0; 
}