PHP - 错误的字母表循环 [英] PHP - Erroneous Alphabet Loop

问题描述

 <？php 
 for（$ i ='a'; $ i< ='z'; $ i ++）{
 echo$ i; 
} 
？> 
  

为什么它的输出是：

abcdefghijklmnopqrstu vwxyz aa ab ac ad ae af
ag ah a a a al al a a a ap ap a ar as as au av aw ax ay az ba bb bc
bd be bf bg bh bi bj bk bl bm bn bo bp bq br bs bt bu bv bw bx by bz
ca cb cc cd ce cf cg ch ci cj ck c c c c c c c c c c c c c c cr cr cs ct cu cv cw
cx cy cz da db dc dd de df dg dh di dj dk dl dm dn do dp dq dr ds dt
du dv dw dx dy dy ez ee ee ee e e e e e e e e e e e e e e e e e
er es et eu ev ew ex ex ... on to yz

但是它的工作方式很好

$ $ $ $ $ $ $ $ $ $ $ $ $ $ $ b回显$ i;
}
？>

循环似乎反复运行直到达到zz。 b
$ b

如果我给 $ i ，它应该可以正常工作，但是只输出a。 b $ b

解决方案

请参阅在字符上的运算符
$ b 变量而不是C的。例如，在PHP和Perl中$ a =
'Z'; $ A ++;将$ a变成'AA'，而C a ='Z';一个++;将a变成
'['（'Z'的ASCII值是90，'['的ASCII值是91'）。请注意，
字符变量可以递增，但不能递减，即使只支持
纯ASCII字符（a-z和A-Z）。
增加/减少其他字符变量不起作用，
原始字符串不变。

Can Anyone Explain me why :

    <?php
    for ($i = 'a'; $i <= 'z'; $i++){
    echo "$i ";
    }
    ?>

Why its Output is :

a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag ah ai aj ak al am an ao ap aq ar as at au av aw ax ay az ba bb bc bd be bf bg bh bi bj bk bl bm bn bo bp bq br bs bt bu bv bw bx by bz ca cb cc cd ce cf cg ch ci cj ck cl cm cn co cp cq cr cs ct cu cv cw cx cy cz da db dc dd de df dg dh di dj dk dl dm dn do dp dq dr ds dt du dv dw dx dy dz ea eb ec ed ee ef eg eh ei ej ek el em en eo ep eq er es et eu ev ew ex... on to yz

But its Working Fine With

    <?php
    for ($i = 'a'; $i != 'aa'; $i++){
    echo "$i ";
    }
    ?>

The loop seems to run over and over again until it reaches "zz".

If I give $i<"aa" it should work fine but instead it outputs only "a".

解决方案

See the manual for the increment operator:

PHP follows Perl's convention when dealing with arithmetic operations on character variables and not C's. For example, in PHP and Perl $a = 'Z'; $a++; turns $a into 'AA', while in C a = 'Z'; a++; turns a into '[' (ASCII value of 'Z' is 90, ASCII value of '[' is 91). Note that character variables can be incremented but not decremented and even so only plain ASCII characters (a-z and A-Z) are supported. Incrementing/decrementing other character variables has no effect, the original string is unchanged.

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