++i 和i++区别

时间：2023-3-10 14:24 作者：小诸葛 分类： JavaScript 正在检查是否收录...
运算规则
代码
<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8" />
        <meta name="viewport" content="width=device-width, initial-scale=1">
        <title></title>
        <style>
            * {
                box-sizing: border-box;
                margin: 0;
                padding: 0;
                font-size: 16px;
                font-weight: bold;

            }

            .box {

                color: #fff;
                border-radius: 8px;
                width: 500px;
                height: 240px;
                background-color: seagreen;
                margin: 20px auto;
                box-shadow: inset -2px 7px 22px #000000;
            }

            input {
                text-align: center;
                padding: 0 15px;
                outline-color: #55aaff;
                border: 0;
                height: 30px;
                box-shadow: 4px 4px 3px #000000;
            }

            #sum1,
            #sum2 {
                width: 150px;
            }

            p {
                margin: 20px;

            }

            #s {
                border: 0;
                padding: 0 10%;
                width: 150px;
                height: 30px;

            }

            #j {
                color: #fff;
                width: 150px;
                line-height: 30px;
            }

            button {
                width: 150px;
                height: 30px;
                border: 0;
                box-shadow: 0px 1px 4px #000000;
            }

            #xs {
                line-height: 30px;
                color: #aa0000;
                width: 150px;
                background-color: #fff;

            }
        </style>
    </head>
    <body>

        <!-- 3. 编程题: 运算完成后计算出a b c d的值（自己写出答案后再打印运算结果，互相验证）（考点：运算符 ++ --）
               let a = 5, b = 7;
               let c = b++ - --a;
               let d = ++a + b--; -->

        <div class="box">
            <p style="padding-top: 50px; ">
                数值：<input type="text" id="sum1" placeholder="请输入数值1">
                数值：<input type="text" id="sum2" placeholder="请输入数值2">
            </p>

            <p>
                过程：<input type="text" id="j" disabled>
                运算：<select id="s">
                    <option>+</option>
                    <option>-</option>
                </select>
            </p>

            <p>
                运行：<button onclick="js()">点击计算</button>
                结果：<input type="text" id="xs" disabled>
            </p>

        </div>

        <script>
            function js() {
                let S = s.value; //定义选择框变量
                let Sum = 0; //定义存储计算结果变量
                let Sum1 = Number(sum1.value); //输入框1
                let Sum2 = Number(sum2.value); //输入框2
                if (isNaN(Sum1) == true || isNaN(Sum2) == true) { //判断参数是否为数字
                    sum1.value = null;
                    sum2.value = null;
                    document.getElementById("xs").value = "参数错误"
                } 
                else if (S == "+" && Sum1 != " " && Sum2 != " ") { //判断运算符
                    Sum = ++Sum1 + Sum2--;
                    xs.value = Sum; //把运算结果赋值给显示框
                    document.getElementById("j").value = "++" + sum1.value + "   " + "+" + "   " + sum2.value + "- -";
                } 
                else if (S == "-" && Sum1 != " " && Sum2 != " ") {
                    Sum = ++Sum1 - Sum2--;
                    xs.value = Sum;
                    document.getElementById("j").value =  "++" +  sum1.value + "   " + "-" + "   " + "- -"+sum2.value;

                } else {
                    sum1.value = null;
                    sum2.value = null;
                    document.getElementById("xs").value = "参数错误"

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