js function:
<script type="text/javascript">
function findaverageL() {
var l1 = document.getElementById('<%= txtqnty.ClientID %>');
var l2 = document.getElementById('<%= txtNCRqty.ClientID %>');
var avgl = document.getElementById('<%= txtOKqnty.ClientID %>');
avgl.value = parseFloat(l1.value) - parseFloat(l2.value);
}
// this function is for validate Number Only. It not allow to entr characters in textbox
function isNumberKey(evt) {
var charCode = (evt.which) ? evt.which : event.keyCode
if (charCode != 46 && charCode > 31
&& (charCode < 48 || charCode > 57))
return false;
return true;
}
</script>
<asp:TextBox ID="txtqnty" runat="server" Text="0" onkeypress="return isNumberKey(event)" onpaste="return false" ondrop="return false" onchange='javascript:findaverageL();'></asp:TextBox>
