0-100包含几个9?

0-100整数字包含几个9?

private void button1_Click(object sender, EventArgs e)        {            int j = 0;            string sum = "";            for (int i = 0; i <= 100;i++ )            {                if (i.ToString().IndexOf('9') > -1)                {                    j = j + 1;                }                sum = sum + i.ToString();            }            MessageBox.Show(j.ToString());            MessageBox.Show(sum.ToString());        }

输出结果:

其中99包含两个9.

共20个9.