<?php

function tester($count, $str){
    $str = "Total count is $count";
}

$count = 0;
$str = "Total count is $count";

// $str === 'Total count is 0';

$str = tester($count, $str); // $str === 'Total count is 1';

$str = tester($count, $str); // $str === 'Total count is 2';

$str = tester($count, $str); // $str === 'Total count is 3';