<!DOCTYPE html>

<html xmlns="http://www.w3.org/1999/xhtml">

<head>

<meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>

    <title>02if.html</title>

    <script>

        var age = parseInt(prompt("請輸入年齡","20"));//prompt跳出輸入框,20為預設輸入數值(回傳值為String),parseInt把傳值轉為數字

        if (isNaN(age))

            document.write("請輸入數字");

        else if (0 < age && age <= 6 || 65 <= age)//記得要加&&,不可以直接用0<age<=6

            document.write("免票");

        else if (6 < age && age <= 25)

            document.write("學生票");

        else if (25 < age && age <= 65)

            document.write("全票");

 

        document.write("<hr>");

 

        var a = 10, b = 20;

        if (a > b)

            document.write("a > b");

        else

            document.write("a&lt;b");//注意「<」的前後需要有空格,不然會出錯(誤以為你要打括號),可以打&lt;取代

 

           </script>

</head>

<body>

 

</body>

</html>

 

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