[CODE]
<form name=form1>
<input name="a" type="text">
+
<input name="b" type="text">
<input type="button" name="Submit" value="=" onClick="add();">
<input name="c" type="text">
</form>
<script language="JavaScript">
function add(){
var a=parseFloat(document.form1.a.value);
var b=parseFloat(document.form1.b.value);
document.form1.c.value=a+b;
return document.form1.c.value;
}
</script>
[/CODE]