""/'' or regex bug

[Duke555]

i have a bug in my code (below) and i cannot work out how to get rid of it.
when i test the code (by uncommenting one of '$sentence = ...') every word that begins with a '$' disappears and 'ay' gets added to where the word is supposed to be. when i change "" to '' all the problems go away. could someone explain to me why this is the case and what is causing it?


thank you very much
=========================================
<?php
//echo "Word provided by the user is: ".$_POST['word']."<br>";

$sentence = $_POST['word'];
/*$sentence = "@#%^##Hello World ?##World ?earner earner earner,? learner $$$learner";*/
/*
$sentence = "@#%^##Hello World $world ?##World ?earner earner earner,? world $world";*/
$sentence = strtolower($sentence);


//echo "converted to lower case: ".$sentence."<br>";

$cleaned_sentence = clean_string($sentence);

echo $cleaned_sentence."<br>";

$translated = translate($cleaned_sentence);

echo "The translated word/sentence into Pig Latin is: ".$translated."<br>";

/****************************************************************************/

function clean_string($sentence_to_be_cleaned) {
$bad_characters = "[^a-zA-Z]";
$new_sentence = ereg_replace($bad_characters, ' ', $sentence_to_be_cleaned);
return $new_sentence;
}

function translate($string_to_translate)
{
// separating a sentence passed into individual words to translate into Pig Latin
// echo "string passed to translate() is: ".$string_to_translate."<br>";

$string = explode(' ', $string_to_translate);

// this regex will be used to check if the first letter is vowel or not
$reg_expression = '(a|e|i|o|u)';

// go through the string passed by INPUT word by WORD
foreach($string as $key=>$word)
{
//if 1st letter of a word is a vowel
if(check_regex($reg_expression, substr($word,0,1)) == TRUE)
{
// concatenate pig latin suffix and a given word to a total string which is going to be returned by the func. in the end
$total_string = $total_string.$word.'\'yay ';
}
// if a character is a ' ' (space) which occurs when any of the @#$? were replaced clean_string() then get rid of it
else if($word == ' ')
{
$word = '';
}
// else - 1st letter is a consonant
else
{
// find, replace the 1st consonant and then concatenate to a string which is going to be returned by
// the function
$consonant = substr($word,0,1);
$temp_string = substr_replace($word, "", 0, 1);
echo $temp_string."---- ";
// concatenate pig latin suffix and a given word to a total string which is going to be returned by the func. in the end
$total_string = $total_string.$temp_string.$consonant."ay"." ";


}
}
return $total_string;
}

function check_regex($myregex, $mystring) {
if (ereg($myregex, $mystring)) {
return TRUE;
}
else {
return FALSE;
}
}
?>