<?php 
function getDateForSpecificDayBetweenDates($startDate, $endDate, $weekdayNumber)
{
    $startDate = strtotime($startDate);
    $endDate = strtotime($endDate);
    $dateArr = array();
    do {
        if (date("w", $startDate) != $weekdayNumber) {
            $startDate += 24 * 3600;
            // add 1 day
        }
    } while (date("w", $startDate) != $weekdayNumber);
    while ($startDate <= $endDate) {
        $dateArr[] = date('Y-m-d', $startDate);
        $startDate += 7 * 24 * 3600;
        // add 7 days
    }
    return $dateArr;
}
$dateArr = getDateForSpecificDayBetweenDates('2015-01-01', '2015-12-31', 1);
// 0 Sun, 1 Mon, etc.
$i = 0;
foreach ($dateArr as $date) {
    echo $date . "</br>";
    $i++;
}
echo $i;
<?php

function getDateForSpecificDayBetweenDates($start, $end, $weekday = 0)
{
    $weekdays = "Sunday,Monday,Tuesday,Wednesday,Thursday,Friday,Saturday";
    $arr_weekdays = explode(",", $weekdays);
    $weekday = $arr_weekdays[$weekday];
    if (!$weekday) {
        die("Invalid Weekday!");
    }
    $start = strtotime("+0 day", strtotime($start));
    $end = strtotime($end);
    $dateArr = array();
    $friday = strtotime($weekday, $start);
    while ($friday <= $end) {
        $dateArr[] = date("Y-m-d", $friday);
        $friday = strtotime("+1 weeks", $friday);
    }
    $dateArr[] = date("Y-m-d", $friday);
    return $dateArr;
}
$dateArr = getDateForSpecificDayBetweenDates("2015-10-01", "2015-10-31", 0);
//0 Sun, 1 Mon, etc.
echo $n = sizeof($dateArr);
$i = 1;
foreach ($dateArr as $date) {
    if ($i < $n) {
        echo "<br>" . $date;
    }
    $i++;
}