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isset()与empty()函数 switch语句改写简易计算器
樱风醉
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693 people have browsed it

一.isset()与 empty()函数

isset()函数

  • isset()函数中0、false、''都认为它们是有值的，返回值是 true
  • null 和 没有这个变量，返回值是 false
  1. $null = null;
  2. $num = 0;
  3. $str = '';
  4. $bool = false;
  6. var_dump(isset($num));  // true
  7. echo '<br>';
  8. var_dump(isset($str)); // true
  9. echo '<br>';
  10. var_dump(isset($bool)); // true
  11. echo '<br>';
  12. var_dump(isset($null)); // false
  13. echo '<br>';
  14. var_dump(isset($no)); //false

empty()函数

  • empty()函数判断变量为空的情况时会返回 true
  • 空字符串'' 数字零0 bool值false null 字符串零'0' 或没有这个变量，都为空，返回值为 true
  1. $str = '';
  2. $num = 0;
  3. $bool = false;
  4. $null = null;
  5. $str0 = '0';
  7. var_dump(empty($str)); // true
  8. echo '<br>';
  9. var_dump(empty($num)); // true
  10. echo '<br>';
  11. var_dump(empty($bool)); // true
  12. echo '<br>';
  13. var_dump(empty($null)); // true
  14. echo '<br>';
  15. var_dump(empty($str0)); // true
  16. echo '<br>';
  17. var_dump(empty($no)); // true

二.switch 语句

  • 用于根据多个不同条件执行不同动作
  1. switch (n)
  2. {
  3. case label1:
  4.     如果 n=label1，此处代码将执行;
  5.     break;
  6. case label2:
  7.     如果 n=label2，此处代码将执行;
  8.     break;
  9. default:
  10.     如果 n 既不等于 label1 也不等于 label2，此处代码将执行;
  11. }

三.switch 语句改写计算器

  1. <!DOCTYPE html>
  2. <html lang="zh-CN">
  3. <head>
  4.     <meta charset="UTF-8">
  5.     <meta http-equiv="X-UA-Compatible" content="IE=edge">
  6.     <meta name="viewport" content="width=device-width, initial-scale=1.0">
  7.     <title>简易计算器</title>
  8. </head>
  9. <body>
  10.     <h2>简易计算器</h2>
  11.     <form action="" method="get">
  12.         <input type="number" name="num1" value="<?= isset($_GET['num1']) ? $_GET['num1'] : ''; ?>">
  13.         <select name="opt" id="">
  14.             <option value="+" <?= isset($_GET['opt']) && $_GET['opt'] == '+' ? 'selected' : ''; ?>>+</option>
  15.             <option value="-" <?= isset($_GET['opt']) && $_GET['opt'] == '-' ? 'selected' : ''; ?>>-</option>
  16.             <option value="*" <?= isset($_GET['opt']) && $_GET['opt'] == '*' ? 'selected' : ''; ?>>×</option>
  17.             <option value="/" <?= isset($_GET['opt']) && $_GET['opt'] == '/' ? 'selected' : ''; ?>>÷</option>
  18.             <option value="%" <?= isset($_GET['opt']) && $_GET['opt'] == '%' ? 'selected' : ''; ?>>%</option>
  19.         </select>
  20.         <input type="number" name="num2" value="<?= isset($_GET['num2']) ? $_GET['num2'] : ''; ?>">
  21.         <input type="submit" value="计算">
  22.     </form>
  23. </body>
  24. </html>
  26. <?php
  28. if(!empty($_GET)){
  29.     $opt = $_GET['opt'];
  30.     $num1 = $_GET['num1'];
  31.     $num2 = $_GET['num2'];
  32.    switch($opt){
  33.         case '+':
  34.             $num = $num1 + $num2 ;
  35.             echo '计算结果：'.$num1.'+'.$num2.'='.$num;
  36.             break;
  37.         case '-':
  38.             $num = $num1 - $num2 ;
  39.             echo '计算结果：'.$num1.'-'.$num2.'='.$num;
  40.             break;
  41.         case '*':
  42.             $num = $num1 * $num2 ;
  43.             echo '计算结果：'.$num1.'×'.$num2.'='.$num;
  44.             break;
  45.         case '/':
  46.             if($num2 == 0){
  47.                 echo '除数不能为0';
  48.             }else{
  49.                 $num = $num1 / $num2 ;
  50.                 echo '计算结果：'.$num1.'÷'.$num2.'='.$num;
  51.             }
  52.             break;
  53.         case '%':
  54.             if($num2 == 0){
  55.                 echo '除数不能为0';
  56.             }else{
  57.                 $num = $num1 % $num2 ;
  58.                 echo '计算结果：'.$num1.'%'.$num2.'='.$num;
  59.             }
  60.             break;
  61.    }
  62. }
  63. ?>

Correcting teacher：PHPzPHPz

Correction status：qualified

Teacher's comments：
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