AnyCard购物平台（字符自动追加.,）

        private void textBox1_TextChanged(object sender, EventArgs e)
        {
            //得到用户输入
            string getStr = textBox1.Text;
            if (getStr.Length <= 14)//最多允许输入9位数字（加两个','和'.'和小数点后两位总共14）
            {
                char[] myChar = getStr.ToCharArray();
                //清除符号
                string clearStr = "";
                foreach (char var in myChar)
                {
                    if (var != '.' && var != ',')
                    {
                        clearStr += var;
                    }
                }
                //转换成Char数组，再颠倒顺序
                char[] clearStrDesc = clearStr.ToCharArray();
                Array.Reverse(clearStrDesc);
                //加符号后的显示（顺序颠倒的）
                string markStrDesc = "";
                //加符号
                for (int i = 0; i < clearStrDesc.Length; i++)
                {
                    if (clearStrDesc.Length == 1 || clearStrDesc.Length == 2)
                    {
                        markStrDesc = clearStr;
                        return;
                    }
                    if (i == 2)
                    {
                        markStrDesc += "." + clearStrDesc[i];
                    }
                    if (i == 5 || i == 8)
                    {
                        markStrDesc += "," + clearStrDesc[i];
                    }
                    if (i != 2 && i != 5 && i != 8)
                    {
                        markStrDesc += clearStrDesc[i];
                    }
                }
                //把加符号的字符串转换为Char数组
                char[] c3 = markStrDesc.ToCharArray();
                //倒回来
                Array.Reverse(c3);
                //显示
                string displayStr = new string(c3);
                textBox1.Text = displayStr;
            }
            else
            {
                string constNum = getStr.Substring(0, 14);
                textBox1.Text = constNum;
            }
        }