January 2021
Intermediate to advanced
505 pages
9h 45m
Chinese
Content preview from PHP编程：第4版
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流程控制语句
｜
51
比较这两者的语法 ：
if (
表达式
) {
正确时的语句
} else {
错误时的语句
}
(
表达式
) ?
正确时的表达式
:
错误时的表达式
最大的区别在于，三元操作符不是一个语句，它只在表达式里面使用。三元操作符的结
果是一个表达式，也可以说是它自己。在前面使用
if
语句的例子中，
echo
语句用在
if
条件里面，而使用三元操作符，
echo
是前面的表达式。
switch
一个变量的值可以决定多种选择（例如，变量储存着用户名，而且你想要为不同的用户
做不同的事情），
switch
语句就是为这种情况而设计的。
switch
语句会将一个表达式的值和
switch
里面所有的情况（
case
）进行比较，如果匹配
到相等的
case
值，则该
case
下面所有的语句都会被执行，直到第一次遇到
break
关键字。
switch
语句如果没有匹配到任何一个
case
，并且提供了一个
default
，则所有
default
关键字下面的语句都会被执行，直到第一次遇到
break
关键字。
假设你写了下面的代码 ：
if ($name == 'ktatroe') {
//
做一些事
}
else if ($name == 'dawn') {
//
做一些事
}
else if ($name == 'petermac') {
//
做一些事
}
else if ($name == 'bobk') {
//
做一些事
}
可以使用
switch
语句替换成下面的语句 ：
switch($name) {
case 'ktatroe':
// ...
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.