Stop calling function if empty - php

Question

how can i stop calling the function if one of my fields are empty? Because i have a function that count the days between two fields, So if one my field is empty the result of count is showing "12,000" something like that.
Example:
$start = ("");
$end =("2017-10-19");
$date = getWorkingDays($start, $end);
This is the function that is used, But whenever the $start is greater than $end i get a wrong result. how can i fix it?
function getWorkingDays($startDate,$endDate ){
// do strtotime calculations just once
$startDate = strtotime($startDate);
$endDate = strtotime($endDate);
//The total number of days between the two dates. We compute the no. of seconds and divide it to 60*60*24
//We add one to inlude both dates in the interval.
$days = ($endDate - $startDate) / 86400 + 0;
$no_full_weeks = floor($days / 7);
$no_remaining_days = fmod($days, 7);
//It will return 1 if it's Monday,.. ,7 for Sunday
$the_first_day_of_week = date("N", $startDate);
$the_last_day_of_week = date("N", $endDate);
// If one of the value is empty it will return "0"
if ($startDate == '' || $endDate == '')
return "0"; // Default value
//---->The two can be equal in leap years when february has 29 days, the equal sign is added here
//In the first case the whole interval is within a week, in the second case the interval falls in two weeks.
if ($the_first_day_of_week <= $the_last_day_of_week) {
if ($the_first_day_of_week <= 6 && 6 <= $the_last_day_of_week) $no_remaining_days--;
if ($the_first_day_of_week <= 7 && 7 <= $the_last_day_of_week) $no_remaining_days--;
}
else {
// (edit by Tokes to fix an edge case where the start day was a Sunday
// and the end day was NOT a Saturday)
// the day of the week for start is later than the day of the week for end
if ($the_first_day_of_week == 7) {
// if the start date is a Sunday, then we definitely subtract 1 day
$no_remaining_days--;
if ($the_last_day_of_week == 6) {
// if the end date is a Saturday, then we subtract another day
$no_remaining_days--;
}
}
else {
// the start date was a Saturday (or earlier), and the end date was (Mon..Fri)
// so we skip an entire weekend and subtract 2 days
$no_remaining_days -= 2;
}
}
//The no. of business days is: (number of weeks between the two dates) * (5 working days) + the remainder
//---->february in none leap years gave a remainder of 0 but still calculated weekends between first and last day, this is one way to fix it
$workingDays = $no_full_weeks * 5;
if ($no_remaining_days > 0 )
{
$workingDays += $no_remaining_days;
}
return $workingDays;
}
$start = ("2017-04-21");
$end = ("2017-04-17");
$date = getWorkingDays($start, $end);
echo $date;

Answer 1

You just need to check if $start and $end are not empty.
Either when calling your function :
$start = ("");
$end =("2017-10-19");
if ($start != '' && $end != '') {
$date = getWorkingDays($start, $end);
} else {
$date = 0; // Default value
}
Or in your function declaration :
function getWorkingDays($start, $end) {
if ($start == '' || $end == '')
return 0; // Default value
/* Here is the rest of your function */
}