0100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.