class Program {
#region 求數列前n項和實例
/**
* 2+22+222+2222+...+222222222 輸入m,n 求出總和sum
* 2(1+11+111+1111+...+111111111)
* 2(123456789)
* An = m + 10^(n-1)
*
* */
int m, n;
int i, temp = 0, sum = 0;
Console.WriteLine("計算 m + mm + mmm + …… + mmmmmmm 最後一項有n個m\n請輸入m n的值\n");
int.TryParse(Console.ReadLine(), out m);
int.TryParse(Console.ReadLine(), out n);
for (i = 0; i < n; i++)
{
temp = temp * 10 + m;
sum += temp;
}
Console.WriteLine("當 m = {0} , n = {1}時,S{2} = {3}\n", m, n, n, sum);
#endregion
}