Q:

how to call a c# function in anchor tag click event

How to call server side function using HTML anchor tag.
Here I showed some example of my code.
HTML
<html xmlns="http://www.w3.org/1999/xhtml"> 
    <head runat="server"> 
         <title>Update</title> 
    </head> 
<body> 
<form id="form1" runat="server"> 
    <div> 
        <a href="" onclick="btnSubmit_Click()">Update</a> 
    </div>  
</form> 
</body> 
</html>

c#
protected void btnSubmit_Click(object sender, EventArgs e) 
{ 
   //Update User Details
} 

A:

Try like this,
create one submit button and hide that
HTML
<html xmlns="http://www.w3.org/1999/xhtml"> 
<head runat="server"> 
    <title>Update</title> 
    <script language="javascript" type="text/javascript"> 
        function fireServerButtonEvent(){ 
            document.getElementById("btnSubmit").click(); 
        } 
    </script> 
</head> 
<body> 
<form id="form1" runat="server"> 
    <div> 
        <asp:button id="btnSubmit" runat="server" text="Submit" xmlns:asp="#unknown">
            onclick="btnSubmit_Click" style="display:none" /></asp:button>
        <a href="" onclick="fireServerButtonEvent()">Update</a> 
    </div> 
</form> 
</body> 
</html>

