PHP-----循环结构

for循环语句

打印金字塔

完整的金字塔

<span  1</span> <span //</span><span 打印金字塔</span>
<span  2</span>     <span $n</span>=25<span ;
</span><span  3</span>     <span for</span>(<span $i</span>=1;<span $i</span><=<span $n</span>;<span $i</span>++<span ){
</span><span  4</span>         <span //</span><span 空格循环</span>
<span  5</span>         <span for</span>(<span $k</span>=1;<span $k</span><=<span $n</span>-<span $i</span>;<span $k</span>++<span ){
</span><span  6</span>             <span echo</span> ' '<span ;
</span><span  7</span> <span         }
</span><span  8</span>         <span //</span><span 字符循环</span>
<span  9</span>         <span for</span>(<span $j</span>=1;<span $j</span><=<span $i</span>*2-1;<span $j</span>++<span ){
</span><span 10</span> 
<span 11</span>             <span if</span>(<span $i</span>==1 || <span $i</span>==<span $n</span><span ){
</span><span 12</span>                 <span echo</span> '.'<span ;
</span><span 13</span> <span             }
</span><span 14</span>             <span else</span><span {
</span><span 15</span>                 <span if</span>(<span $j</span>==1 || <span $j</span>==<span $i</span>*2-1<span ){
</span><span 16</span>                     <span echo</span> '.'<span ;
</span><span 17</span>                 }<span else</span><span {
</span><span 18</span>                     <span echo</span> ' '<span ;
</span><span 19</span> <span                 }
</span><span 20</span> <span             }
</span><span 21</span> <span         }
</span><span 22</span>         <span /*</span>
<span 23</span> <span         for($j=1;$j<=($i-1)*2+1 ; $j++) { 
</span><span 24</span> <span             echo '.';
</span><span 25</span> <span         }</span><span */</span>
<span 26</span>         <span echo</span> '<br/>'<span ;
</span><span 27</span> 
<span 28</span>     }

switch语句：

<span  1</span> <span /*</span><span $a="1";
</span><span  2</span> <span     switch ($a) {
</span><span  3</span> <span         case 1:
</span><span  4</span> <span             echo $a;
</span><span  5</span> <span             break;
</span><span  6</span>         
<span  7</span> <span         default:
</span><span  8</span> <span             echo "错误";
</span><span  9</span> <span             break;
</span><span 10</span> <span     }
</span><span 11</span> <span     //自动转换字符串和数字</span>

switch选择语句中遇到布尔值时的处理：

<span  1</span> <span $b</span>=<span true</span><span ;
</span><span  2</span>     <span switch</span>(<span $b</span><span ){
</span><span  3</span>         <span case</span> <span false</span>:
<span  4</span>             <span echo</span> "不匹配"<span ;
</span><span  5</span>             <span break</span><span ;
</span><span  6</span>         <span //</span><span 代表非false的值都可以为true-----自动转换类型</span>
<span  7</span>         <span case</span> "1":
<span  8</span>             <span echo</span> "成功匹配"<span ;
</span><span  9</span>             <span break</span><span ;
</span><span 10</span>         <span default</span>:
<span 11</span>             <span echo</span> "ko"<span ;
</span><span 12</span> <span     }
</span><span 13</span>     <span //</span><span 1.default语句不论顺序都是最后执行，如果没有匹配到其他的case，那么就执行default语句
</span><span 14</span> <span     //2.如果没有break语句，那么就会输出下一个case的结果，直到有break为止。</span>

while循环和do..while循环：

<span  1</span> <span /*</span><span while循环
</span><span  2</span> <span     $i=0;
</span><span  3</span> <span     while($i<10){
</span><span  4</span> <span         echo "paxster<br>".$i;
</span><span  5</span> <span         $i++;
</span><span  6</span> <span     }
</span><span  7</span> <span     //do..while循环--------先执行再判断，至少执行一次
</span><span  8</span> <span     /*$do=0;
</span><span  9</span> <span     do{
</span><span 10</span> <span         echo '<br />Paxster';
</span><span 11</span> <span         $do=$do+1;
</span><span 12</span> <span     }while($do<8);</span><span */</span>

while循环和switch选择语句的结合：

常量：

<span 1</span> <span //</span><span 定义常量-----两种方法</span>
<span 2</span>     <span define</span>('TAX',200<span );
</span><span 3</span>     <span echo</span><span  TAX; 
</span><span 4</span> 
<span 5</span>     <span const</span> Tab=100<span ;
</span><span 6</span>     <span echo</span> Tab;

编写简易计算器：

step1:编写输入界面

<span  1</span> <html>
<span  2</span> <head>
<span  3</span>     <title></title>
<span  4</span>     
<span  5</span> </head>
<span  6</span> <body>
<span  7</span> 
<span  8</span> <form action="CAL.php" method="get">
<span  9</span>     <input type="text" placeholder="输入一个数" name="num1">
<span 10</span>     <input type="text" placeholder="输入一个数" name="num2">
<span 11</span>     <select name="operation">
<span 12</span>         <option value="+">+</option>
<span 13</span>         <option value="-">-</option>
<span 14</span>         <option value="*">*</option>
<span 15</span>         <option value="/">/</option>
<span 16</span>     </select>
<span 17</span>     <input type="submit" value="计算">
<span 18</span> </form>
<span 19</span> </body>
<span 20</span> </html>

step2:写计算后台代码

<span  1</span> <?<span php
</span><span  2</span>     <span $num1</span>=<span $_REQUEST</span>['num1'<span ];
</span><span  3</span>     <span $num2</span>=<span $_REQUEST</span>['num2'<span ];
</span><span  4</span> 
<span  5</span>     <span $operation</span>=<span $_REQUEST</span>['operation'<span ];
</span><span  6</span>     <span $res</span>=0<span ;
</span><span  7</span> 
<span  8</span>     <span switch</span>(<span $operation</span><span ){
</span><span  9</span>         <span case</span> '+':
<span 10</span>             <span $res</span>=<span $num1</span>+<span $num2</span><span ;
</span><span 11</span>             <span break</span><span ;
</span><span 12</span>         <span case</span> '-':
<span 13</span>             <span $res</span>=<span $num1</span>-<span $num2</span><span ;
</span><span 14</span>             <span break</span><span ;
</span><span 15</span>         <span case</span> '*':
<span 16</span>             <span $res</span>=<span $num1</span>*<span $num2</span><span ;
</span><span 17</span>             <span break</span><span ;
</span><span 18</span>         <span case</span> '/':
<span 19</span>             <span $res</span>=<span $num1</span>/<span $num2</span><span ;
</span><span 20</span>             <span break</span><span ;
</span><span 21</span>         <span default</span>:
<span 22</span>             <span echo</span> '输入有误'<span ;
</span><span 23</span> <span     }
</span><span 24</span> 
<span 25</span>     <span echo</span> '结果是'.<span $res</span><span ;
</span><span 26</span> ?>

continue语句：跳过本次循环后面的代码。可以指定跳出指定的层数，例如continue 2；表示跳出两层，类似于break 2;

goto语句：和c语言一样，跳转到有标签的代码处，中间的代码不会执行，直接忽略。

<span  1</span> <span //</span><span goto语句
</span><span  2</span> <span     //i只执行一次</span>
<span  3</span>     <span for</span>(<span $i</span>=0,<span $j</span>=50;<span $i</span><100;<span $i</span>++<span ){
</span><span  4</span>         <span while</span>(<span $j</span>--<span ){
</span><span  5</span>             <span if</span>(<span $j</span>==17) goto <span end</span><span ;
</span><span  6</span> <span         }
</span><span  7</span> <span     }
</span><span  8</span>     <span echo</span> 'i=$i'<span ;
</span><span  9</span>     <span end</span>:
<span 10</span>     <span echo</span> 'i='.<span $i</span>.'j='.<span $j</span>;