if和elseif有什么区别？ [英] What's the difference between if and elseif?

问题描述

这应该是一个简单的问题。我有一个简单的if / else语句：

This should be a simple question. I have a simple if/else statement:

    <?php
    // TOP PICTURE DEFINITIONS
    if ( is_page('english') ) {
        $toppic = 'page1.png';
    }
    if ( is_page('aboutus') ) {
        $toppic = 'page1.png';
    }
    if ( is_page('newspaper') ) {
        $toppic = 'page1.png';
    }
    else {
        $toppic = 'page1.png';
    }
?>

与^^^有不同之处：

<?php
    // TOP PICTURE DEFINITIONS
    if ( is_page('english') ) {
        $toppic = 'page1.png';
    }
    elseif ( is_page('aboutus') ) {
        $toppic = 'page1.png';
    }
    elseif ( is_page('newspaper') ) {
        $toppic = 'page1.png';
    }
    else {
        $toppic = 'page1.png';
    }
?>

我应该提到这是进入Wordpress的。直到现在，我已经使用了第一部分（没有其他，只是一系列'ifs'），它的确有效。我只是想知道区别是什么。

I should mention that this is going into Wordpress. And until now, I've used the first part (no elseif, just a series of 'ifs'), and it works. I was just curious to know what the difference was.

谢谢！
Amit

Thanks! Amit

推荐答案

是的。如果满足 if / else 控件中的条件，则将省略其余检查。 否则如果只是一个嵌套的，如果在 else 内！

Yes. If a condition in an if/else control is satisfied, the rest of the checks will be omitted. else if is just a nested if inside an else!

if ( is_page('english') ) { // if true, other statements are skipped
    $toppic = 'page1.png';
}
elseif ( is_page('aboutus') ) {
    $toppic = 'page1.png';
}
elseif ( is_page('newspaper') ) {
    $toppic = 'page1.png';
}
else {
    $toppic = 'page1.png';
}

但在一系列中如果 s，所有这些都将被测试。

But in a series of ifs, all of them will be tested.

if ( is_page('english') ) {
    $toppic = 'page1.png';
}
if ( is_page('aboutus') ) { // will be tested no matter what the outcome
                            // of the previous if statement was
    $toppic = 'page1.png';
}
if ( is_page('newspaper') ) { // the same here
    $toppic = 'page1.png';
}
else {
    $toppic = 'page1.png';
}

因此，如果您正在检查诸如数字奇偶校验的属性，无论是奇数还是偶数，如果一个人满意，你为什么还要费心去检查其他条件。这是浪费资源。因此，以下代码要好得多

So, if you're checking a property such as parity of a number, it's either odd or even, why do you want to bother checking other conditions if one is satisfied. It's a waste of resources. Therefore, the following code is much better

if(number_is_odd) {
}
else { // if it's not odd, it's even for sure
}

比

if(number_is_odd) {
}

if(!number_is_odd) {
}

因为前者检查条件一次而后者检查两次。具有两种以上状态的条件也是如此。

Because the former checks the condition once whilst the latter does it twice. The same thing goes for conditions with more than two states.

这篇关于if和elseif有什么区别？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！