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PHP4用户手册:流程控制-for_PHP

Jun 01, 2016 pm 12:38 PM
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手册

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for 循环是PHP中非常复杂的循环。它的行为象C语言中的一样。以下是循环的语法:

 


for (expr1; expr2; expr3) statement

 

第一个表达式(expr1)是循环无条件开始的值。

在每次反复开始,表达式expr2 被计算。如果值为TRUE,则继续循环,执行嵌套的语句。如果值为FALSE,执行循环以后的

在每次反复,表达式expr3 被计算(执行)。

每个表达式都可以为空。expr2 为空则意味着循环将不确定的运行(PHP 隐暗认为它为真,象C语言一样)。 这不可能想你想的那样结束,你可以使用break语句去代替for事实表达式去结束循环。

考虑以下的例子。它们将显示1至10的数字:

 


/* 例 1 */

for ($i = 1; $i     print $i;
}

/* 例 2 */

for ($i = 1;;$i++) {
    if ($i > 10) {
        break;
    }
    print $i;
}

/* 例 3 */

$i = 1;
for (;;) {
    if ($i > 10) {
        break;
    }
    print $i;
    $i++;
}

/* 例 4 */

for ($i = 1; $i

 

当然,从第一个例子看出是简略的(或是第四个),但是你可以发现有很多的机会你可以使用空表达式。

PHP 仍然支持循环的“冒号语法”。

 


for (expr1; expr2; expr3): statement; ...; endfor;

 

另我的语言有一个 foreach 语句去操作数组或散列。PHP 3 中没有这样的构造;PHP 4 有(参见 foreach)。在PHP 3中,人可以用while、list() 和each() 函数去完成相同的功能。参见这些函数的文档。

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