<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title>计算器的实现</title>
</head>
<style type="text/css">
   
    #sDiv {
        text-align: center;
        border: solid 1px;
        width: 300px;
        border-radius: 10px;
        background-color: aqua;
        margin: 20px auto;
        background-image: url("http://b-ssl.duitang.com/uploads/item/201506/09/20150609224048_RCQPf.jpeg") ;
    }

    #t {
        border: solid 1px;
        width: 260px;
        border-radius: 10px;
        margin-top: 10px;
        margin-bottom: 10px;
        font-size: 20px;
    }

    input[type=button] {
        border-radius: 15px;
        width: 55px;
        height: 30px;
        margin: 2px;
        font-size: 20px;
    }

    #equ {
        width: 260px;
        font-size: 30px;
        margin-bottom: 10px;
    }
</style>

<body>
<div id="sDiv">

    <input type="text" name="t" id="t" value=""/><br/>
    <input type="button" name="" value="1" onclick="calCulate(this.value)"/>
    <input type="button" name="" value="2" onclick="calCulate(this.value)"/>
    <input type="button" name="" value="3" onclick="calCulate(this.value)"/>
    <input type="button" name="" value="4" onclick="calCulate(this.value)"/><br/>
    <input type="button" name="" value="5" onclick="calCulate(this.value)"/>
    <input type="button" name="" value="6" onclick="calCulate(this.value)"/>
    <input type="button" name="" value="7" onclick="calCulate(this.value)"/>
    <input type="button" name="" value="8" onclick="calCulate(this.value)"/><br/>
    <input type="button" name="" value="9" onclick="calCulate(this.value)"/>
    <input type="button" name="" value="0" onclick="calCulate(this.value)"/>
    <input type="button" name="" value="." onclick="calCulate(this.value)"/>
    <input type="button" name="" value="C" onclick="calCulate(this.value)"/><br/>
    <input type="button" name="" value="+" onclick="calCulate(this.value)"/>
    <input type="button" name="" value="-" onclick="calCulate(this.value)"/>
    <input type="button" name="" value="*" onclick="calCulate(this.value)"/>
    <input type="button" name="" value="/" onclick="calCulate(this.value)"/><br/>
    <input type="button" name="" id="equ" value="=" onclick="calCulate(this.value)"/>
</div>
<script type="text/javascript">

    function calCulate(val) {

        console.log("===>",val);

        var num = document.getElementById("t");
        switch (val) {
            case "=":
                num.value = eval(num.value);

                break;

            case "C":
                num.value = "";
                break;

            default:
                num.value = num.value + val;
                break;
        }


    }
</script>
</body>
</html>