PHP date/time questions

[Mike Kypriotis]

I have a program keeping the shifts of workers (e.g. at 12/1/2012 X worker worked the 8:00-16:00 shift). Shifts duration is variable meaning that the admin defines its duration so a couple of questions
a) How can i calculate the hours in each shift? (the shifts start/end either at :00 or :30 e.g. 8:00-16:30 or 16:30-18:30) meaning that 16:30-18:00 is 1 and a half hour (or 3 halfs of hour -which is the format i will be saving it) or 8:00-16:00 is 16*30min. Note that shifts like 16:00-1:00 or 20:00-03:00 also exists.
b) given that in my database i have how many hours of each day each worker worked, i wanna check how many hours a given worker worked this week (do not want each worker to pass the 40h a week limit)
any ideas?

[Luuk]

This will calculate the number of half-hours are between start and end:

<?php
    function halfhours($from,$to) {
        $u1=substr($from,0,2);
        $m1=substr($from,3,2);
        $u2=substr($to,0,2);
        $m2=substr($to,3,2);
 
        echo "$u1:$m1 $u2:$m2 \n";
        $d = ($u2-$u1)*2;
        if ($d<=0) { $d=$d+48; }
        if ($m1==30) { $d = $d-1; }
        if ($m2==30) { $d = $d+1; }
 
        return $d;
    }
 
    $from="16:30";
    $to="18:00";
    echo "Number of half-hours between $from and $to is: ".halfhours($from,$to)." <br>\n";
 
    $from="20:00";
    $to="03:00";
    echo "Number of half-hours between $from and $to is: ".halfhours($from,$to)." <br>\n";
?>
 

To calculatie how many hours someone has worked more info is needed.
Probably you are storing this in a database?

[programDragon]

Why not just use the time() function and figure out your hours from the seconds.