Add alphabet to spaces in string

[DaemonProjects]

im trying to display a string with php but what I want is to add letters to all the blank spaces in the sentence in alphabetical order.

Example:

string:
Hello world this is a test

new string:
Helloaworldbthiscisdaetest

so all the way to z. and if the string has more spaces than in the alphabet then I want to start back to a then to z

what I have so far

<?php
function do_offset($level){
    $offset = "";             // offset for subarry 
    for ($i=1; $i<$level;$i++){
    $offset = $offset . "<td></td>";
    }
    return $offset;
}

function show_array($array, $level, $sub){
$getit = 0;
    if (is_array($array) == 1){          // check if input is an array
       foreach($array as $key_val => $value) {
	   	$getit = $getit + 1;
           $offset = "";
           if (is_array($value) == 1){   // array is multidimensional
           echo "<tr>";
           $offset = do_offset($level);
           echo $offset . "<td>" . $key_val . "</td>";
           show_array($value, $level+1, 1);
           }
           else{                        // (sub)array is not multidim
           if ($sub != 1){          // first entry for subarray
               //echo "<tr>";
               $offset = do_offset($level);
           }
           $sub = 0; 
		   if ($getit > 40) {
		   	if ($value == " ") {
				echo $offset . "<td width=\"120\" align=\"center\" onDblClick=\"style.backgroundColor='#000000';\">".strtolower(genstring(1))."</td></tr>\n";
			} else {
		   		echo $offset . "<td width=\"120\" align=\"center\" onDblClick=\"style.backgroundColor='#000000';\">".strtolower($value)."</td></tr>\n"; 
			}
			$getit = 0;
		   } else {
		  	 if ($value == " ") {
		   		echo $offset . "<td width=\"120\" align=\"center\" onDblClick=\"style.backgroundColor='#000000';\">".strtolower(genstring(1))."</td>\n"; 
			 } else {
			 	echo $offset . "<td width=\"120\" align=\"center\" onDblClick=\"style.backgroundColor='#000000';\">".strtolower($value)."</td>\n"; 
			 }
		   }

       //echo "</tr>\n";
       }
   } //foreach $array
}  
else{ // argument $array is not an array
    return;
}
}
function genstring($length){  

srand((double)microtime()*1000000);   
$cons = array("a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z");     
$num_cons = count($cons);  

for($i = 0; $i < $length; $i++){    
	//$getnewstr .= $cons[rand(0, $num_cons - 1)]; 
	$getnewstr .= $cons[rand(0, $num_cons - 1)];
} 
return substr($getnewstr, 0, $length);  

}  

function html_show_array($array){
  echo "<table cellspacing=\"0\" border=\"0\" width=\"640\" align=\"center\">\n";
  echo "<tr>";
  show_array($array, 1, 0);
  echo "</tr></table>\n";
}

$str = 'Hello world this is a test sentence to check out how this php script works. This is only a test.';
$chars = preg_split('//', $str, -1, PREG_SPLIT_NO_EMPTY);
//print_r($chars);
html_show_array($chars);
?>

code above works but it does put the letters in alphabetical order.

thanks
D

[Weedpacket]

You can use [man]preg_match_all[/man] to find all the spaces; adding the PREG_OFFSET_CAPTURE will include their locations in the string in the returned array.
You can then loop through that changing the characters with $string[$position]=$char;