Print given string in all combinations of uppercase and lowercasecharacters

Given a string we need to print the string with all possible combinations of the uppercase and lowercase characters in the string.

So given a string "abc", we need to print the following:
ABC
ABc
AbC
Abc
aBC
aBc
abC
abc

Solution is a simple recursive approach where we call the function again and again once with a character in lower case and another time with the same character in upper case. The code is similar to what we would write for all permutations of a string.

lowerUpper("abc", 0, 3);

function lowerUpper($str, $start, $strLength) {
  if ($start === $strLength) {
    var_dump($str);
    return;
  }
    
  $str[$start] = strtoupper($str[$start]);
  lowerUpper($str, $start+1, $strLength);
    
  $str[$start] = strtolower($str[$start]);
  lowerUpper($str, $start+1, $strLength);
}