<?php

$str = "mary had a little lamb and she loved it so";
 
$pieces = explode(" ", $str);
 $array = [];
 
foreach($pieces as $piece){
		//echo $piece;
 
		for($i = 0; $i < count($piece); $i++){
 
			$letter = strtoupper($piece[0]);
 
			$newLetter = substr_replace($piece, $letter, 0, 1);
 
			array_push($array, $newLetter);
		}
	}
	$result = implode(" ", $array);
	echo $result;