test

test code

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

public partial class AddTextboxValue : System.Web.UI.Page
{
    
    protected void Page_Load(object sender, EventArgs e)
    {

    }
    protected void txt1_TextChanged(object sender, EventArgs e)
    {
        if((!string.IsNullOrEmpty(txt1.Text)) && (!string.IsNullOrEmpty(txt2.Text)))
        {
            txt3.Text = (Convert.ToInt32(txt1.Text) + Convert.ToInt32(txt2.Text)).ToString();
        }
    }
    protected void txt2_TextChanged(object sender, EventArgs e)
    {
        if ((!string.IsNullOrEmpty(txt1.Text)) && (!string.IsNullOrEmpty(txt2.Text)))
        {
            txt3.Text = (Convert.ToInt32(txt1.Text) + Convert.ToInt32(txt2.Text)).ToString();
        }
    }
    
}

test reply