Add a random character to a string after every character

Question

How can I add random character from [A-Za-z0-9] / or - to a string every second character? e.g. input:

Hello_world!

output:

H3e7l2l-o2_aWmocr9l/db!s

Edit: Here is what I've tried, however without the line below the one marked Here that throws an error

Uncaught TypeError: implode(): Argument #2 ($array) must be of type ?array, string given in....

I guess it's because a fragment of $char is not an array. After I'd added the line below Here to "convert" the string to array another error appeared:

Uncaught TypeError: str_repeat(): Argument #1 ($string) must be of type string, array given in...

<?php
$string = "Hello_World!";
$length = strlen($string);
$string = str_split($string, 2);
$chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789/-";

//Here 
$chars = (is_array($chars)) ? $chars : [$chars];

for($i = 0; $i < ($length / 2); $i++){
  $char = substr(str_shuffle(str_repeat($chars, 1)), 0, 1);
  $added = implode($string[$i], $char);
}

echo $string;

?>

score 1 · Answer 1 · answered Oct 28 '22 at 17:10

<?PHP
  $str =  "Hello World!";
  
  $new_string = '';
  for($i =0; $i < strlen($str); $i++){ // loop through the string
     $new_string .= $str[$i]; // add character to new string
     $new_string .= getRandomCharacter(); // add the random character to new string
  }
  echo $new_string;
  
  function getRandomCharacter(){
     $random_characters = 'abcdefghijklmnopqrstuvwxyz'
                 .'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
                 .'0123456789!@#$%^&*()';
    $index= rand(0, (strlen($random_characters)- 1) ); // generates random character index from the given set.
    return $random_characters[$index];
  }
  
?>

score 1 · Accepted Answer · answered Oct 28 '22 at 17:18

$str = 'Hello_world!';
$chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789/-';
$result = array_reduce(str_split($str),
  fn($carry, $item)=>$carry.=$item.$chars[rand(0,strlen($chars)-1)], '');
print_r($result);

str_split splits your input string into characters, then array_reduce recombines them with the random chars added.

score 1 · Answer 3 · answered Dec 26 '22 at 11:27

Since your inputs are both strings AND the pool of random characters contains only single-byte characters, this task can be directly achieved with no array functions and no concatenation.

Call for a random letter to be inserted in the original string after each letter via preg_replace_callback().

Code: (Demo)

$str = 'Hello_world!';
$chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789/-';
$max = strlen($chars) - 1;

echo preg_replace_callback(
    '/.\K/',
    fn() => $chars[rand(0, $max)],
    $str
);

\K tells the regex engine to forget the previously matched character. This results in no characters being lost -- the random letter is added at the zero-width position after each character.

If you were dealing with input arrays, then it might be worth reading Implode array with array of glue strings for a clever vprintf() trick.

Add a random character to a string after every character

3 Answers3