How to validate US Zip Code in C#.net

       

      /// <summary>

        /// This Text event is use for USA-Zip code validation in C#.Net.

        /// </summary>

        /// <param name="sender"></param>

        /// <param name="e"></param>

        protected void txtZipcode_TextChanged(object sender, EventArgs e)

        {

            if (!string.IsNullOrEmpty(txtZipcode.Text))

            {

                string replaceLength = txtZipcode.Text;

                txtZipcode.Text = replaceLength.Replace("-", "");

                string findLength = txtZipcode.Text;

                int length = findLength.Length;

                if (length >= 5 && length <= 11)

                {

                    if (length == 5)

                    {

                        txtZipcode.Text = txtZipcode.Text + "-0000";

                    }

                    else

                    {

                        txtZipcode.Text = txtZipcode.Text.Substring(0, 5) + "-" +

                                            txtZipcode.Text.Substring(5, txtZipcode.Text.Length - 5);

                        string zipL = txtZipcode.Text;

                        int zipLength = zipL.Length;

                        if (zipLength == 10)

                        {

                            txtZipcode.Text = txtZipcode.Text.Substring(0, 10);

                        }

                        else

                        {

                            for (int i = 0; i < 10 - zipLength; i++)

                            {

                                txtZipcode.Text += "0";

                            }

                        } 

                    }

                     lblZip.Visible = false;

                }

                else

                {

                    lblZip.Visible = true;

                    lblZip.Text = "Invalid Zip!";

                    txtZipcode.Text = string.Empty;

                }

         }

  }