whats the cs code for save account created date and last password updated date

Well...GETDATE is the SQL function for the current date and has nothing to do with C#, but it works, yes - and it's a reasonably sensible function to use because it means all timestamps are set using the same clock.
So all you have to do is set up a simple SQL query to do an UPDATE:

UPDATE MyTable SET LastLoginDate=GETDATE() WHERE UserId=...

and supply your actual user identification information instead of the ellipsis.

The C# code is pretty trivial - it's exactly the same as your code for an INSERT, and (hopefully) uses a parameterized query - but I don't know which of the many ways to do that you are using, so I'll leave the exact implementation to you!


here is my login code where did i put "UPDATE MyTable SET LastLoginDate=GETDATE() WHERE UserId=... " code in

protected void login_btn_Click(object sender, EventArgs e)
    {
        int cnt = 0;

        //  SqlDataAdapter ad1 = new SqlDataAdapter(@"select Id  from UserReg WHERE Name='" + TextBox1.Text + "' AND Password='" + TextBox2.Text + "'", con);
        //  DataTable dt = new DataTable();



        SqlCommand cmd;
        SqlDataReader dr;
        cmd = new SqlCommand("select Id  from UserReg WHERE Name='" + username.Text + "' AND Password='" + password.Text + "'");

        con.Open();
        cmd.Connection = con;
        cmd.ExecuteNonQuery();
        dr = cmd.ExecuteReader();
        while (dr.Read())
        {

            //  ad1.Fill(dt);
            cnt = Convert.ToInt32(dr["Id"].ToString());
        }

        if (cnt > 0)
        {
            Response.Redirect("profile.aspx?id=" + cnt); //Response.Redirect("veinpage.aspx?id=" + cnt);
        }

        else
        {
            loginchk.Text = "Invalid username or password";
            this.loginchk.ForeColor = Color.Red;
        }
        
    }
}

Oh dear...

Forget what you are trying to do with the updates, and have a good hard look at your code. Because what you have there my friend, is code that is supremely dangerous, and wide open to abuse.
For example, did you know I could log into your system without any password, or indeed username, for anywhere in the world? As anyone I wanted to? Or I could just delete your whole database without logging in? It's called SQL Injection, and you are wide, wide open to it.
In addition, you are storing passwords in clear text! Do you not read the news? Do you not understand how dangerous that is?

You seriously need to fix both of those - it isn't complex - and I would also recommend that you stop using a "home brewed" login system and look at Membership[^] - it's easy to follow and implement, and it gives you a lot better security than you are trying to implement.
But for goodness sake, use parameterised queries at all times - or your best friend will delete your DB just to see the look on your face!
Think I'm joking?
Try to log in with this username and no password:

x' OR Id > 0;--