> For the complete documentation index, see [llms.txt](https://phper.shujuwajue.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://phper.shujuwajue.com/ji-chu/liu-cheng-kong-zhi-yu-ju.md).

# 流程控制与条件判断

## 流程控制语句

**3中流程控制语句**  <br>

* 使用for循环
* 使用foreach循环
* 使用while、list()、each()组合循环

**介绍：**

* for循环，只能遍历索引数组，
* foreach可以遍历索引和关联数组
* 联合使用list(),each()和while循环同样可以遍历索引和关联数组

**区别**  <br>

* list(),each()和while组合不会reset()操作（之前有对数组进行了指针的操作，则使用此方式，则不会重置数组，而是在这个指针往后循环，就会出现数据不完整）
* forreach遍历会对数组进行resrt()操作

示例：

```php
<?php

$data = array('a','b','c');
next($data);  //改变了数组的指针指向

echo 'while循环' . '<br>';
while(list($k,$v) = each($data)){ 
    echo $k . '=' . $v. '<br />'; 
} 

echo 'for循环' . '<br>';
for($i=0;$i< count($data); $i++) {
    echo $i . '=' . $data[$i] . '<br>';
}

echo 'foreach循环' . '<br>';
foreach($data as $k => $v) {
    echo $k . '=' . $v . '<br>';
}
```

输出结果：

```
while循环
1=b
2=c
for循环
0=a
1=b
2=c
foreach循环
0=a
1=b
2=c
```

## 条件判断语句

### **switch...case..语句**

switch后面的控制表达式的数据类型只能是**整型、浮点类型或者字符串**  <br>

continue语句作用到switch的作用类似break;

跳出switch外的循环，可以使用continue2 或者break2；

示例：

```
<?php

$a = 10;
for($i=0;$i< 10;$i++) {
    switch($i){
        case 5:
            break 2;
        default:
            break;
    }

    echo $i.'<br>';
}
```

结果：

```
0
1
2
3
4
```

**效率：**  <br>

如果条件判断比较复杂或者在一个很多次的循环中，那么用switch语句可能会快一些

### php如何优化多个if..else语句的情况？

* 1.尽量把可能性大的判断往前放
* 2.如果条件判断比较复杂或者在一个很多次的循环中，并且判断是一个是整型、浮点类型或者字符串换用switch..case..


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