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php switch case用法与实例教程

Jun 08, 2016 pm 05:27 PM
break case default nbsp switch

switch 语句和 elseif 语句的比较 在 switch 语句中,条件只求一次,然后和每个 case 比较,而在 elseif 语句中,条件会再次求值。如果你的条件比较复杂,或者是多次循环,用 switch 语句速度会更加快些。

<script>ec(2);</script>

php switch 循环,通常处理复合式的条件判断,每个子条件,都是 case 指令部分,通常为变量名称。而 case 后的 exprN,通常表示变量值。冒号后则为符合该条件要执行的部分。注意要用 break 跳离循环。

switch与if 区别是

 

用 if 循环就很麻烦了。当然在设计时,要将出现机率最大的条件放在最前面,最少出现的条件放在最后面,可以增加程序的执行效率,Switch 语句可以避免冗长的 if..elseif..else 代码块。


switch (expr) {
     case expr1:            //注意这里是冒号:
       statement1;         //这里是分号;
       break;                   //这里是分号;
     case expr2:
       statement2;
       break;
       :
       :
     default:
       statementN;
       break;
}

工作原理:

对表达式(通常是变量)进行一次计算
把表达式的值与结构中 case 的值进行比较
如果存在匹配,则执行与 case 关联的代码
代码执行后,break 语句阻止代码跳入下一个 case 中继续执行
如果没有 case 为真,则使用 default 语句

看个实例
*/
$i =5;
switch( $i )
{
 case 1:
  echo '1';
  break;
 case 2:
  echo '2';
  break;
 case 3:
  echo '5';
  break;
 case 4:
  echo $i;
  break;
 default:
  echo 'cc';
}

//switch方法

switch( $i )
{
 case 1:
 case 2:
 case 3:
  $c =555;
  break;
 default:
  $c =2;
}

//看看if else

if( $i ==1 or $i ==3 or $i ==2 )
{
 $c =555;
}
else
{
 $c =2;
}
/*
从上面实例可以看出if else与switch case 比较区别如文章开头所有了。
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