老师我这个4/0报出来的和视频上的怎么不一样

来源：3-1 四则运算的实现

weixin_慕少7311860

2022-09-26 11:53:28

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <link rel="stylesheet" type="text/css" href="1.css">
    <script type="text/javascript" src="1.js"></script>
</head>

<!-- //初始化  加载 页面刷新 -->
<body onload="init()">
    <div id="div1">
        <div id="div2">
            <input type="text"   name="num" id="num"/>
        </div>
        <div id="div3">
            <input type="button" value="c" name="" id=""/>
            <input type="button" value="←" name="" id=""/>
            <input type="button" value="+/-" name="" id=""/>
            <input type="button" value="/" name="" id=""/>
            <input type="button" value="1" name="" id="n1"/>
            <input type="button" value="2" name="" id=""/>
            <input type="button" value="3" name="" id=""/>
            <input type="button" value="*" name="" id=""/>
            <input type="button" value="4" name="" id=""/>
            <input type="button" value="5" name="" id=""/>
            <input type="button" value="6" name="" id=""/>
            <input type="button" value="-" name="" id=""/>
            <input type="button" value="7" name="" id=""/>
            <input type="button" value="8" name="" id=""/>
            <input type="button" value="9" name="" id=""/>
            <input type="button" value="+" name="" id=""/>
            <input type="button" value="0" name="" id=""/>
            <input type="button" value="." name="" id=""/>
            <input type="button" value="=" name="" id=""/>
            <input type="button" value="m" name="" id=""/>

           
        </div>
    </div>
   
</body>

</html>

function init(){
    var num=document.getElementById("num");
    num.value=0;
    num.disabled="disabled";
    // var n1=document.getElementById("n1");
    // n1.onclick=function(){
    //     alert("123");
    // }
    var oButton=document.getElementsByTagName("input");
    var btn_num1;
    var fh;
    for(var i=0;i<oButton.length;i++){
        oButton[i].onclick=function(){
            if(isNumber(this.value)){
                // num.value=(num.value+this.value)*1;
                if(isNull(num.value)){
                    num.value=this.value;
                }else{
                    num.value=num.value+this.value;
                }
            }else{
                // alert("fei");
                var btn_num=this.value;
               
                switch(btn_num){
                    case "+":
                        btn_num1=parseInt(num.value);
                        num.value=0;
                        fh="+"
                        break;
                    case "-":
                        btn_num1=parseInt(num.value);
                        num.value=0;
                        fh="-"
                        break;
                    case "*":
                        btn_num1=parseInt(num.value);
                        num.value=0;
                        fh="*"
                        break;
                    case "/":
                        btn_num1=parseInt(num.value);
                        num.value=0;
                        fh="/"
                        break;
                    case ".":
                        alert("2222");
                        break;
                    case "←":
                        alert("2222");
                        break;
                    case "c":
                        alert("2222");
                        break;
                    case "+/-":
                        alert("2222");
                        break;
                    case "=":
                        switch(fh){
                            case "+":
                                num.value=btn_num1+parseInt(num.value);
                                // console.log(bth_num1)
                                break;
                            case "-":
                                num.value=btn_num1-parseInt(num.value);
                                // console.log(bth_num1)
                                break;
                            case "*":
                                num.value=btn_num1*parseInt(num.value);
                                // console.log(bth_num1)
                                break;
                            case "/":
                                if(parseInt(num.value==0)){
                                    alert("除数不能是0")
                                    num.value=0;
                                }else{
                                    num.value=btn_num1/parseInt(num.value);
                                }
                               
                                // console.log(bth_num1)
                                break;
                        }
                        break;
                             
                }
            }
        }
    }
}
/* 验证文本框是否为空或者0 */
function isNull(n){
    if(n=="0" || n.length==0){
        return true;
    }else{
        return false;
    }
}



function isNumber(n){
    // if(isNaN(n)){
    //     return true; //参数n是数字
    // }else{
    //     return false; //参数n不是数字
    // }
   
    return !isNaN(n);
}      


// isNaN:不能转换为数字:ture,可以转为成数字是false

*{
    margin:0px;
    padding:0px;
}
div{
    width: 170px;
}
#div1{
    top: 60px;
    left: 100px;
    position: absolute;
}
input[type="button"]{
    width: 30px;
    margin-right: 5px;
}
input[type="text"]{
    width: 147px;
    text-align: right;
    background-color: #fff;
    border: 1px solid;
}

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