Decrementing alphabetical values

Question

I\'m trying to figure out how to shift a bunch of letter values in an array down one step. For example, my array contains values (\"d\", \"e\", \"f\", \"g\", \"h\") and I wa

Answer 1

If you need to decrement Excel-like variables ('A', 'AA', ...), here's the function I came to. It doesn't work with special characters but is case insensitive. It returns null if you try to decrement 'a' or 'A'.

function decrementLetter($char) {
     $len = strlen($char);
     // last character is A or a
     if(ord($char[$len - 1]) === 65 || ord($char[$len - 1]) === 97){ 
          if($len === 1){ // one character left
               return null;
           }
           else{ // 'ABA'--;  => 'AAZ'; recursive call
               $char = decrementLetter(substr($char, 0, -1)).'Z';
            }
     }
     else{
         $char[$len - 1] = chr(ord($char[$len - 1]) - 1);
     }
     return $char;
}