include() vs require() on PHP

PHP provides four functions which enable you to insert code from other files.
* include()
* require()
* include_once()
* require_once()

All four can take a local file or URL as input. None of them can import a remote file.

require() and include() functions are virtually similar in their function except for the way they handle an irretrievable resource. include() and include_once() provide a warning if the resource cannot be retrieved and try to continue execution of the program if possible. require() and require_once functions provide stop processing the page if they cannot retrieve the resource.

Why include_once() and require_once() ?

The include_once() and require_once() functions are handy in situations where multiple files may reference the same included code.

For example:

File A.php includes File B.php and C.php
File B.php includes File C.php

File C.php has been included twice, so the interpreter would print an error. Since a function cannot be redefined once it’s declared, this restriction can help prevent errors.

If both File A.php and File B.php use include_once() or require_once() to import File C.php, no errors would be generated. PHP would understand that you only want one instance of the code in File C and would not try to redeclare the functions.

It is best to use require_once() to include files which contain necessary code and include_once() to include files that contain content which the program can run without e.g. HTML, CSS, etc.

PHP Array Functions

Array is a Most useful Data Storage in Most of the Programming Languages   Some of unknown array build in functions in php.
                                PHP Array Functions

array_diff (arr1, arr2 …)

array_­filter (arr, function)

array_flip (arr)

array_­int­ersect (arr1, arr2 …)

array_­merge (arr1, arr2 …)

array_pop (arr)

array_push (arr, var1, var2 …)

array_­reverse (arr)

array_­search (needle, arr)

array_walk (arr, function)

count (count)

in_array (needle, haystack)

Get all sunday date of current Year Using PHP

Following function return array of list of Sunday's Date of the Current Year in PHP.

<?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);
}

$year   = date("Y");

$dateArr = getDateForSpecificDayBetweenDates($year.'-01-01', $year.'-12-31', 0);

print "<pre>";
print_r($dateArr);

?>

And if you want to get any other day of  week then just change value of weekday. I have pass 0 value into the function to get all Sunday of the current year.

Note : Pass weekdays value between 0  to 6.