Send mail and increase the number for each user

    protected void btnKatil_Click(object sender, EventArgs e)
    {
        Label1.Text = TextBox1.Text;
        Label2.Text = TextBox2.Text;
        Label3.Text = TextBox3.Text;
 
        int seatNumber = 1;  //i want to increase this number each time and send mail
        
        MailMessage mail = new MailMessage();  
 
        mail.To.Add(TextBox3.Text);
        mail.From = new MailAddress("abcx@gmail.com");
        mail.Subject = "MailSubject" ;
        mail.Body = "Dear " + TextBox1.Text + " " + TextBox2.Text + " Seat Number : " + seatNumber.ToString();
        mail.IsBodyHtml = true;
        
        SmtpClient client = new SmtpClient("smtp.gmail.com", 587);
        client.EnableSsl = true;
 
        NetworkCredential credentials = new NetworkCredential("abcx@gmail.com", "password");
        client.Credentials = credentials;
        try
        {
            client.Send(mail);
 
            seatNumber++;
 
        }
        
        catch (Exception hata)
        {
            Response.Write(hata);
        }
    }