<!DOCTYPE html>
<html lang="ko">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>CALC</title>
<script>
// 숫자와 연산기호 입력
function input_num(calc_num){
document.getElementById("formula").value += calc_num;
}
// 사칙연산 수행
function calculate(result){
var formula = document.getElementById("formula").value;
result = eval(formula);
document.getElementById("result").value = result;
}
// 초기화
function reset(){
document.getElementById("formula").value = null;
document.getElementById("result").value = null;
}
</script>
</head>
<body>
<div align='center'>
<input type="text" name="formula" id="formula" size="30"><br> <!-- size:30 == 180pt -->
<input type="text" name="result" id="result" size="30"><br>
<input type="button" value="초기화" style="width: 90pt;" onclick="reset()">
<input type="button" value="=" size="15" id="result_btn" style="width: 90pt;" onclick="calculate()"><br>
<input type="button" style="width: 45pt;" id="btn" value="7" onclick="input_num('7')">
<input type="button" style="width: 45pt;" id="btn" value="8" onclick="input_num('8')">
<input type="button" value="9" style="width: 45pt;" id="btn" onclick="input_num('9')">
<input type="button" value="+" style="width: 45pt;" id="btn" onclick="input_num('+')"><br>
<input type="button" value="4" style="width: 45pt;" id="btn" onclick="input_num('4')">
<input type="button" value="5" style="width: 45pt;" id="btn" onclick="input_num('5')">
<input type="button" value="6" style="width: 45pt;" id="btn" onclick="input_num('6')">
<input type="button" value="-" style="width: 45pt;" id="btn" onclick="input_num('-')"><br>
<input type="button" value="1" style="width: 45pt;" id="btn" onclick="input_num('1')">
<input type="button" value="2" style="width: 45pt;" id="btn" onclick="input_num('2')">
<input type="button" value="3" style="width: 45pt;" id="btn" onclick="input_num('3')">
<input type="button" value="*" style="width: 45pt;" id="btn" onclick="input_num('*')"><br>
<input type="button" value="0" style="width: 60pt;" id="btn" onclick="input_num('0')">
<input type="button" value="." style="width: 60pt;" id="btn" onclick="input_num('.')">
<input type="button" value="/" style="width: 60pt;" id="btn" onclick="input_num('/')"><br>
</div>
</body>
</html>