c++入门题。求sn=a+aa+aaa+…+n个a。大神们看看我的程序哪里有问题

 图片分辨率太低，看不清。
写一个给你
int a = 2;
int n = 5;

int b = a;
int sum = 0;
for (int i = 1; i < 5; i++)
{
sum += b;
b *= 10;
b += a;
}
cout << sum;

#include
using namespace std;
int main()
{
int a ;
int n;
cin>>a;
cin>>n;
int b = a;
int sum = 0;
for (int i = 1; i <= n; i++)
{
sum += b;
b *= 10;
b += a;
}
cout << sum;
return 0;
}

for (int i = 1; i < 5; i++)
->
for (int i = 1; i <= n; i++)