PHP Function To Get Character Number - php

Question

How can I write a function that gives me number of the character that is passed to it
For example, if the funciton name is GetCharacterNumber and I pass B to it then it should give me 2
GetCharacterNumber("A") // should print 1
GetCharacterNumber("C") // should print 3
GetCharacterNumber("Z") // should print 26
GetCharacterNumber("AA") // should print 27
GetCharacterNumber("AA") // should print 27
GetCharacterNumber("AC") // should print 29
Is it even possible to achieve this ?

Answer 1

There is a function called ord which gives you the ASCII number of the character.
ord($chr) - ord('A') + 1
gives you the correct result for one character. For longer strings, you can use a loop.
<?php
function GetCharacterNumber($str) {
$num = 0;
for ($i = 0; $i < strlen($str); $i++) {
$num = 26 * $num + ord($str[$i]) - 64;
}
return $num;
}
GetCharacterNumber("A"); //1
GetCharacterNumber("C"); //3
GetCharacterNumber("Z"); //26
GetCharacterNumber("AA"); //27
GetCharacterNumber("AC"); //29
GetCharacterNumber("BA"); //53
?>

Answer 2

Not very efficient but gets the job done:
function get_character_number($end)
{
$count = 1;
$char = 'A';
$end = strtoupper($end);
while ($char !== $end) {
$count++;
$char++;
}
return $count;
}
echo get_character_number('AA'); // 27
demo
This works because when you got something like $char = 'A' and do $char++, it will change to 'B', then 'C', 'D', … 'Z', 'AA', 'AB' and so on.
Note that this will become the slower the longer $end is. I would not recommend this for anything beyond 'ZZZZ' (475254 iterations) or if you need many lookups like that.
An better performing alternative would be
function get_character_number($string) {
$number = 0;
$string = strtoupper($string);
$dictionary = array_combine(range('A', 'Z'), range(1, 26));
for ($pos = 0; isset($string[$pos]); $pos++) {
$number += $dictionary[$string[$pos]] + $pos * 26 - $pos;
}
return $number;
}
echo get_character_number(''), PHP_EOL; // 0
echo get_character_number('Z'), PHP_EOL; // 26
echo get_character_number('AA'), PHP_EOL; // 27
demo

Answer 3

Use range and strpos:
$letter = 'z';
$alphabet = range('a', 'z');
$position = strpos($alphabet, $letter);
For double letters (eg zz) you'd probably need to create your own alphabet using a custom function:
$alphabet = range('a', 'z');
$dictionary = range('a','z');
foreach($alphabet AS $a1){
foreach($alphabet AS $a2) {
$dictionary[] = $a1 . $a2;
}
}
Then use $dictionary in place of $alphabet.

Answer 4

Here is the full code that does what you want.
Tested it and works perfectly for the examples you gave.
define('BASE', 26);
function singleOrd($chr) {
if (strlen($chr) == 1) {
return (ord($chr)-64);
} else{
return 0;
}
}
function multiOrd($string) {
if (strlen($string) == 0) {
return 0;
} elseif (strlen($string) == 1) {
return singleOrd($string);
} else{
$sum = 0;
for($i = strlen($string) - 1; $i >= 0; $i--) {
$sum += singleOrd($string[$i]) * pow(BASE, $i);
}
}
return $sum;
}

Answer 5

I think ord should be a more efficient way to have your number :
$string = strtolower($string);
$result = 0;
$length = strlen($string);
foreach($string as $key=>$value){
$result = ($length -$key - 1)*(ord($value)-ord(a)+1);
}
and result would contain what you want.