Probleme mktime() en php

Bonjour,
j'ai un probleme en php dans une application open source. ca me donne erreur ds ces lignes de code

1)
$yesterday = mktime(0,0,0,$month,$day,$year) - 24*60*60;
Warning: mktime() expects parameter 4 to be long, string given in H:\wamp\www\timesheet.php\daily.php on line 33

2)
$tomorrow = mktime(0,0,0,$month,$day,$year) + 24*60*60;
Warning: mktime() expects parameter 4 to be long, string given in H:\wamp\www\timesheet.php\daily.php on line 34

3)
echo strftime("%A %B %d, %Y", mktime(0,0,0,$month, $day, $year))
l'erreur est "Warning: mktime() expects parameter 4 to be long, string given in H:\wamp\www\timesheet.php\daily.php on line 118
Thursday January 01, 1970"""