string birthday = this.txtDate.Text;//(1990-01-28)

        //截取成19900128

         string num1 = birthday.Substring(0,1);//从索引为0的数开始，截取一位字符

         string num2 = birthday.Substring(1,1);

         string num3 = birthday.Substring(2,1);

         string num4 = birthday.Substring(3,1);

         string num5 = birthday.Substring(5,1);

         string num6 = birthday.Substring(6,1);

         string num7 = birthday.Substring(8,1);

         string num8 = birthday.Substring(9,1);