<html>
<head>
<title>덧셈/뺄셈 버튼으로 구현하기</title>
< type="text/">
var exp=0;

function show(obj)
{
 var temp = obj.value;
 cal(temp);
 document.getElementById("condition").value += temp;
}
function erase()
{ 
 var erase='';
 document.getElementById("condition").value = erase;
 document.getElementById("result").value = erase;
}

function cal(a)
{
 exp += a;
}
function compute()
{
 if(eval(exp)=="")
 {
  alert("입력형식이 잘못 되었습니다. 다시 입력해 주세요") ;  <-------------------------------------- 2/0 했을때 이게 왜 안뜰까요?
 }
 
 document.getElementById("result").value = eval(exp);
 
 
 exp=0;
}

</>
</head>
<body>
덧셈/뺄셈 버튼 계산기
<br>
<form>
<input type="button" value="1" ="show(this)">
<input type="button" value="2" ="show(this)">
<input type="button" value="3"  ="show(this)"><br>
<input type="button" value="4"  ="show(this)">
<input type="button" value="5"  ="show(this)">
<input type="button" value="6"  ="show(this)"><br>
<input type="button" value="7"  ="show(this)">
<input type="button" value="8"  ="show(this)">
<input type="button" value="9"  ="show(this)"><br>
<input type="button" value="0"  ="show(this)">
<input type="button" value="+" ="show(this)">
<input type="button" value="-" ="show(this)">
<input type="button" value="*" ="show(this)">
<input type="button" value="/" ="show(this)"><br><br>

<input type="button" value="계산하기" ="compute()">
<input type="button" value="다  시" ="erase()"><br>

상태<input type="text" readonly id="condition"><br>
계산결과<input type="text" readonly id="result">
</form>
</body>
</html>