PHP 中的 if/Elseif 语句答案

【问题标题】：If/Elseif statement in PHPPHP 中的 if/Elseif 语句
【发布时间】：2012-05-06 02:59:33
【问题描述】：

我们正在尝试为变量 $day 创建 if/elseif 语句。我们在与此 PHP 关联的 HTML 代码中定义了变量及其值。我会将 PHP 部分粘贴到此页面。问题是结果页面只给出“$day = 1”的响应。有谁知道此代码中的错误会导致这种情况发生？我们也尝试使用两个等号，但结果更糟！

echo "<p>";
                if ($day = 1) {
                    echo "Sunday Funday! What COMMITMENT to going out!";
                } elseif ($day = 2) {
                    echo "The start of what's sure to be a rough week. Drink away your sorrows.";
                } elseif ($day = 3) {
                    echo "Epic night! SO many themes at the bars!";
                } elseif ($day = 4) {
                    echo "Hump day!! But seriously, what are you doing...? Aren't you too hungover from last night?";
                } elseif ($day = 5) {
                    echo "Thirsty Thursday!! It's close enough to the weekend... right?";
                } elseif ($day = 6) {
                    echo "It's Friiiiiiday, Friiiiiiiday, Gotta get down on Friiiiiiiiiday!";
                } elseif ($day = 7) {
                    echo "It's FRATurday! Go have some fun!";

            }

【问题讨论】：

你肯定需要 2 个等号，因为 = 是赋值
您想专门使用 if/else 吗？这种情况下最好使用switch，
您确实需要使用==。 “让情况变得更糟”是什么意思？
看来你需要花更少的时间在酒吧里，花更多的时间在你的代码上；）
第一个= 是赋值运算符，== 是要在if 中使用的条件运算符。同样对于您的逻辑switch/case 方法我会更合适。

标签： php html if-statement

【解决方案1】：

当您打算使用比较 == 时，您正在使用赋值 =。

Assignment 计算在右侧，所以

if ($day = 1)

和

一样

if (1)

由于these rules与

if (true)

这应该可以解释为什么程序的行为如此，当然您现在知道如何修复它了。但如果你使用switch 声明会更好：

switch($day) {
    case 1:
        echo "Sunday Funday! What COMMITMENT to going out!";
        break;
    case 2:
        echo "The start of what's sure to be a rough week.";
        break;
    // etc etc
}

【讨论】：

当我们添加两个等号时，整个echo语句从结果页面中消失了。
那么问题显然不是比较，而是$day 不等于您正在测试的任何值。您可以使用var_dump($day) 来查看它实际上是什么。

【解决方案2】：

您正在分配 (=)。您需要一个逻辑相等 (==)。

if ($day == 1) {
  echo "Sunday Funday! What COMMITMENT to going out!";
}

查看comparison 和logical operators。还有switch() statement。

【讨论】：

【解决方案3】：

如果要检查的条件列表很长，则通常不希望编写一长串 if / else 语句。而是尝试使用switch 块，甚至是array 映射：

 $map = array(
    1 => "Sunday Funday! What COMMITMENT to going out!",
    2 => "The start of what's sure to be a rough week. Drink away your sorrows.",
    3 => "Epic night! SO many themes at the bars!",
    4 => "...",
 );

这样代码就变得非常简单了：

 echo $map[ $day ];

（理想情况下会使用isset 检查。但在开发阶段，PHP 足够聪明，可以提示缺少条目。如果输入值已经被约束/断言，则无论如何都不需要。）

【讨论】：

【解决方案4】：

你想让所有的条件都像这样

            if ($day == 1) {
                echo "Sunday Funday! What COMMITMENT to going out!";
            } elseif ($day == 2) {
                echo "The start of what's sure to be a rough week. Drink away your sorrows.";
            } elseif ($day == 3) {
                echo "Epic night! SO many themes at the bars!";
            } elseif ($day == 4) {
                echo "Hump day!! But seriously, what are you doing...? Aren't you too hungover from last night?";
            } elseif ($day == 5) {
                echo "Thirsty Thursday!! It's close enough to the weekend... right?";
            } elseif ($day == 6) {
                echo "It's Friiiiiiday, Friiiiiiiday, Gotta get down on Friiiiiiiiiday!";
            } elseif ($day == 7) {
                echo "It's FRATurday! Go have some fun!";

        }

【讨论】：

【解决方案5】：

比较运算符是== 而不是=。

还可以尝试这种查找表方法，在这种情况下更简洁：

$day_msg = array(
    1 => "Sunday Funday! What COMMITMENT to going out!",
    2 => "The start of what's sure to be a rough week. Drink away your sorrows.",
    3 => "Epic night! SO many themes at the bars!",
    4 => "Hump day!! But seriously, what are you doing...? Aren't you too hungover from last night?",
    5 => "Thirsty Thursday!! It's close enough to the weekend... right?"
    6 => "It's Friiiiiiday, Friiiiiiiday, Gotta get down on Friiiiiiiiiday!",
    7 => "It's FRATurday! Go have some fun!"
);
echo "<p>";
echo $day_msg[$day];

【讨论】：

【解决方案6】：

您首先认为是对的，您需要两个等号。

【讨论】：