Question

For example:

$myString = "Hello World";

I want to put random characters into it, so it becomes something like this:

$myString = "~!H@e#llo$*Wo-rld+";

Thanks

Answer 1

naive algorithm:

$len=strlen($myString); // we will not recalc it
$allowed=array('!','~');
for(int $i=0;$i<$countOfChars;++i){
    $x=rand(0,$len); //put after $x characters;
    $char=$allowed[array_rand($allowed)];
    $myString=substr($myString,0,$x).$char.substr($myString,$x);
    ++$len; 
}

But I think you should forget about this idea and you other way to solve your problem