Question

How to show an error messages or data validation messages in Asp.net with c# language.
Please guide me.

Answer 1

Markup:

<asp:Button ID="Button1" runat="server" Text="Button" OnClick="Button1_Click" />

Code-behind:

protected void Button1_Click(object sender, EventArgs e)
{
    ClientScript.RegisterStartupScript(
        this.GetType(), "myalert", "alert('" + errorText + "');", true);
}

or

 Response.Write(
     @"<SCRIPT LANGUAGE=""JavaScript"">alert('" + errorText + "')</SCRIPT>");