간단한 소스의 자바스크립트 계산기

<style type="text/css">
<!--
	.btn{font-weight:bold; font-size:9pt; background-color:white; padding-top:3px;width:40}
//-->
</style>

<script language="JavaScript">
<!--
	function cal(num){
		myform.screen.value += num;
	}

	function answer(){
		try{
			myform.screen.value = eval(document.myform.screen.value);
		}catch(e){alert('잘못된 연산오류 ㅋ')}
	}

	function clearcal(){
		myform.screen.value = "";
	}
//-->
</script>

<form name="myform">
<table border="0" bgcolor="#eeeeee" cellspacing="0" cellpadding="5" style="border-width:1px; border-color:black; border-style:solid;" align="center">
	<tr>
	<td height="0" bgcolor="#E2E2E2"><input type="text" name="screen" size="23"> </td>
	</tr>
	<tr>
	<td>
	<input type="button" value=" 7 " onclick="cal('7')" class="btn">
	<input type="button" value=" 8 " onclick="cal('8')" class="btn">
	<input type="button" value=" 9 " onclick="cal('9')" class="btn">
	<input type="button" value=" + " onclick="cal('+')" class="btn">
	</td>
	</tr>
	<tr>
	<td>
	<input type="button" value=" 4 " onclick="cal('4')" class="btn">
	<input type="button" value=" 5 " onclick="cal('5')" class="btn">
	<input type="button" value=" 6 " onclick="cal('6')" class="btn">
	<input type="button" value=" * " onclick="cal('*')" class="btn">
	</td>
	</tr>
	<tr>
	<td>
	<input type="button" value=" 1 " onclick="cal('1')" class="btn">
	<input type="button" value=" 2 " onclick="cal('2')" class="btn">
	<input type="button" value=" 3 " onclick="cal('3')" class="btn">
	<input type="button" value=" / " onclick="cal('/')" class="btn">
	</td>
	</tr>
	<tr>
	<td>
	<input type="button" value=" 0 " onclick="cal('0')" class="btn">
	<input type="button" value=" . " onclick="cal('.')" class="btn">
	<input type="button" value=" C " onclick="clearcal()" class="btn">
	<input type="button" value=" = " onclick="answer()" class="btn">
	</td>
	</tr>
</table>
</form>

<p align="center">[ 자바스크립트 계산기 ]<p>