截取字符串

          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);