Same as above checkbox option in ASP Web Application

I want to implement the checkbox which on clicking will copy the text value of 5 one textbox to other textbox.

This is my code.

<script type="text/javascript" lang="javascript">
$(document).ready(function () {
    function SameAsMailing() {
        document.getElementById('<%= txtMName.ClientID %>').value = document.getElementById('<%= txtCName.ClientID %>').value;
    }
</script>
<input type="checkbox" name="chkSameAsMailing" id="chkSameAsMailing" onclick="SameAsMailing(this)" />