How to validate a Cell Number in Windows foms

Validating a cellnumber textbox in Windows Form usinr c#

First Add a textbox and button on windows form

Keep name of textbox as textcellno

Double click the button and write below code

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;

namespace WindowsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            String str=Convert.ToString(textcellno.Text);
           
            if(str .Length ==10)
           {
  
              
                    String strcell=String.Empty;
                      for(int i=0;i<10;i ++)
                       {
                            if(Char.IsDigit(str[i]))
                              {
                              
                                }
                             else
                                {
                                     MessageBox.Show("Invalid cellNo");
                                     break;
                                 }
                        }

                        MessageBox.Show("you cell Number is valid:" + str);
            }
            else
            {
                  MessageBox.Show("CellNo Should Contain exactly 10 Digits");
             }
  
             }
        }
    }