PHP条件语句(if else/switch)语法与示例

<?php
if (date("D") == "Sat") echo " http://www.111cn.net提醒你周末了，狂欢去";
?>

<?php
if (file_exists("/usr/local/lib/php3.ini")) {
  echo "以下是 PHP3 的配置文件<p><pre>n";
  readfile("/usr/local/lib/php3.ini");
  echo "</pre>n";
}
?>

<?php
if ($a > $b) {
  echo "a 比 b 大";
} elseif ($a == $b) {
  echo  "a 等于 b";
} else {
  echo "a 比 b 小";
}
?>

<?php
switch ($d=date("D"))
{
case "Mon";
  echo "周一";
  break;
case "Tue";
  echo "周二";
  break;
case "Wed";
  echo "周三";
  break;
case "Thu";
  echo "周四";
  break;
case "Fir";
  echo "周五";
  break;
case "Sat";
  echo "周六";
  break;
case "Sun";
  echo "周日";
  break;
}
?>

<?php
echo "<a href='solution.php?action=add'>增加www.111cn.net</a><br><br>";
echo "<a href='solution.php?action=del'>删除</a><br><br>";
echo "<a href='solution.php?action=search'>查找</a><br><br>";
echo "<a href='solution.php?action=update'>更新</a>";
?>

<?php
$action=$_GET["action"];

switch ($action)
{
 case "add":
 echo "现在可以实现增加功能！";
 break;
 case "del":
 echo "现在可以实现删除功能！";
 break;
 case "search":
 echo "现在可以实现查询功能！";
 break;
 case "update":
 echo "现在可以实现更新功能！";
 break;
}
?>

class Dollar {
  protected $amount;
 
  public function __construct($amount=0) {
    $this->amount = (float)$amount;
  }
 
  public function getAmount() {
    return $this->amount;
  }
 
  public function add($dollar) {
    return new Dollar($this->amount + $dollar->getAmount());
  }
}

<?php

//抽象策略角色《为接口或者抽象类，给具体策略类继承》
interface Strategy
{
    public function computePrice($price);
}
 
//具体策略角色-普通会员策略类
class GenernalMember implements Strategy
{
    public function computePrice($price)
    {
        return $price;
    }
}
 
//具体策略角色-中级会员策略类
class MiddleMember implements Strategy
{
    public function computePrice($price)
    {
        return $price * 0.8;
    }
}
 
//具体策略角色-高级会员策略类
class HignMember implements Strategy
{
    public function computePrice($price)
    {
        return $price * 0.7;
    }
}
 
//环境角色实现类
class Price
{
    //具体策略对象
    private $strategyInstance;
   
    //构造函数
    public function __construct($instance)
    {
        $this->strategyInstance = $instance;
    }
   
    public function compute($price)
    {
        return $this->strategyInstance->computePrice($price);
    }
}
 
//客户端使用
$p = new Price(new HignMember());
 
$totalPrice = $p->compute(100);
 
echo $totalPrice; //70

<?php

//观察者
interface IObserver
{
 public function notify();
}
 
//定义可以被观察的对象接口
interface IObservable
{
 public function addObserver($observer);
}
 
//实现IObservable接口
class MessageSystem Implements IObservable
{
 private $_observers = array();
 
 public function addObserver($observer)
 {
  $this->_observers = $observer;
 }
 
 public function doNotify()
 {
  foreach($this->_observers as $o)
  {
   $o->notify();
  }
 }
}
 
//实现IObserver接口
class User Implements IObserver
{
 public function __construct($username)
 {
  echo "我是新用户{$username}<br/>";
 }
 //通知观察者方法
 public function notify()
 {
  echo '欢迎新用户';
 }
}
 
//使用
$u = new MessageSystem();
 
$u->addObserver(new User('小明'));
//$u->addObserver(new User('小红'));
//$u->addObserver(new User('小黑'));
 
$u->doNotify();

2.摘自PHPCHINA的一个不错例子：

/**
* 定义观察接口
*/
interface Subject
{
    public function Attach($Observer); //添加观察者
    public function Detach($Observer); //踢出观察者
    public function Notify(); //满足条件时通知观察者
    public function SubjectState($Subject); //观察条件
}
 
/**
* 观察类的具体实现
*/
class Boss Implements Subject
{
    public $_action;
   
    private $_Observer;
   
    public function Attach($Observer)
    {
        $this->_Observer[] = $Observer;
    }
   
    public function Detach($Observer)
    {
        $ObserverKey = array_search($Observer, $this->_Observer);
       
        if($ObserverKey !== false)
        {
            unset($this->_Observer[$ObserverKey]);
        }
    }
   
    public function Notify()
    {
        foreach($this->_Observer as $value )
        {
            $value->Update();
        }
    }
   
    public function SubjectState($Subject)
    {
        $this->_action = $Subject;
    }
}
 
/**
* 抽象观察者
*
*/
abstract class Observer
{
    protected $_UserName;
   
    protected $_Sub;
   
    public function __construct($Name,$Sub)
    {
        $this->_UserName = $Name;
        $this->_Sub = $Sub;
    }
   
    public abstract function Update(); //接收通过方法
}
 
/**
* 观察者
*/
class StockObserver extends Observer
{
    public function __construct($name,$sub)
    {
        parent::__construct($name,$sub);
    }
   
    public function Update()
    {
        echo $this->_Sub->_action.$this->_UserName." 你赶快跑...";
    }
}
 
$huhansan = new Boss(); //被观察者
 
$gongshil = new StockObserver("三毛",$huhansan); //初始化观察者
 
$huhansan->Attach($gongshil); //添加一个观察者
$huhansan->Attach($gongshil); //添加一个相同的观察者
$huhansan->Detach($gongshil); //踢出基中一个观察者
 
$huhansan->SubjectState("警察来了"); //达到满足的条件
 
$huhansan->Notify(); //通过所有有效的观察者

<?php
$a=100;
$b="";
$c=null;
//isset检查
echo "isset","$a=$a",isset($a)?"define":"www.111cN.net undefine","rn";
echo "isset","$b=$b",isset($b)?"define":"undefine","rn";
echo "isset","$c=$c",isset($c)?"define":"undefine","rn";
unset($b);
echo "isset","$b",isset($b)?"define":"undefine","rn";
$b=0;
echo "rnrn";
 
//empty检查
echo "empty","$a=$a",!empty($a)?"no empty":"empty","rn";
echo "empty","$b=$b",!empty($b)?"no empty":"empty","rn";
echo "empty","$c=$c",!empty($c)?"no empty":"empty","rn";
unset($b);
echo "empty","$b",!empty($b)?"no empty":"empty","rn";
$b=0;
echo "rnrn";
 
//is_null检查
echo "is_null","$a=$a",!is_null($a)?"no null":"null","rn";
echo "is_null","$b=$b",!is_null($b)?"no null":"null","rn";
echo "is_null","$c=$c",!is_null($c)?"no null":"null","rn";
unset($b);
echo "is_null","$b",is_null($b)?"no null":"null","rn";

<?php

$test=0;

if($test==''){
 echo '<br />在php中，0即为空'; //被输出
}

if($test===''){
 echo '<br />在php中，0即为空'; //不被输出
}

if($test==NULL){
 echo '<br />在php中，0即为空'; //被输出
}

if($test===NULL){
 echo '<br />在php中，0即为空'; //不被输出
}

if($test==false){
 echo '<br />在php中，0即为空'; //被输出
}

if($test===false){
 echo '<br />在php中，0即为空'; //不被输出
}

?>

function eq($v1, $v2) {
if($v1 == $v2 && gettype($v1) == gettype($v2)) {
return 1;
} else {
return 0;
}
}