77

Given any character from a to z, what is the most efficient way to get the next letter in the alphabet using PHP?

Mathias Bynens
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7 Answers7

144

The most efficient way of doing this in my opinion is to just increment the string variable.

$str = 'a';
echo ++$str; // prints 'b'

$str = 'z';
echo ++$str; // prints 'aa'

As seen incrementing 'z' give 'aa' if you don't want this but instead want to reset to get an 'a' you can simply check the length of the resulting string and if its >1 reset it.

$ch = 'a';
$next_ch = ++$ch; 
if (strlen($next_ch) > 1) { // if you go beyond z or Z reset to a or A
 $next_ch = $next_ch[0];
}
codaddict
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  • @Mathias there was a minor error with mixing up the pre and post incrementing. Change it to `$b = ++$a;` – nickf Apr 20 '10 at 08:03
  • @Mathias: My bad...you should be using pre-increment as: `$b=++$a;` @nickf: Thanks :) – codaddict Apr 20 '10 at 08:04
  • Your code sample is incorrect. `$next_ch = $ch++;` will not store the incremented value in `$next_ch`, but *will* in fact increment `$ch`. Confused me there for a sec :) Great tip though, I didn’t know this was even possible. Definitely the most efficient way of doing it! – Mathias Bynens Apr 20 '10 at 08:05
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    you should take the locale into account when doing this. The alphabet is not the same for everybody. – Elzo Valugi Nov 24 '10 at 09:40
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    Is there any way to get previous letter? -- not working – itsazzad Oct 14 '14 at 07:30
  • @itsazzad it seems you must use `chr(ord($ch)-1)` – SlimDeluxe Jan 05 '18 at 09:07
20

It depends on what you want to do when you hit Z, but you have a few options:

$nextChar = chr(ord($currChar) + 1); // "a" -> "b", "z" -> "{"

You could also make use of PHP's range() function:

$chars = range('a', 'z');  // ['a', 'b', 'c', 'd', ...]
nickf
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8

Well, it depends what exactly you want to do with the "edge cases". What result do you expect when the character is z or Z? Do you want the next letter of the same case, or just the next letter, period?

Without knowing the answer to that, for the very basic case, you can just do this:

$next_character = chr(ord($current_character) + 1);

But when you're at Z this will give you [, and z will give you {, according to ASCII values.

Edited as per comment:

If you need the next character of the same case, you can probably just add simple checks after the line above:

if ($next_character == '[')
    $next_character = 'A';
else if ($next_character == '{')
    $next_character = 'a';

These are very simple operations, I really wouldn't worry about efficiency in a case like this.

Chad Birch
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5

How about using ord() and chr()?

<?php
    $next = chr(ord($prev)+1);
?>
Anax
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3
$val = 'z';
echo chr((((ord($val) - 97) + 1) % 26) + 97);

Nice and easy :-)

Mathias Bynens
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DoXicK
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2

Since I only care about lowercase characters in this case, I'll use the following code, based on the answers posted here:

function nextLetter(&$str) {
 $str = ('z' === $str ? 'a' : ++$str);
}

Thanks for the help, guys!

Mathias Bynens
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0

Create an array of all letters, search for existing letter and return its next letter. If you reach the last letter return first letter.

user325894
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