จองห้องพักข้ามเดือนคำนวนออกมาติดลบ จะเขียนแบบใหนดีคะให้คลอบคลุมการทำงาน

<script language ="javaScript">
function goHist(a)
{ history.go(a);}
</script>
<?php
//session_start() ;
if(!session_is_registered("login_true")) {
echo "<meta http-equiv='refresh' content='0;url=index.php'>" ;
exit() ;
}
include("config.php") ;
mysql_select_db($dbname) ;

$AMem_ID = $_POST["AMem_ID"];
$Staff_ID = $_POST["Staff_ID"];
$bookType = $_POST["bookType"];
$checkin = $_POST["checkin"];
$checkout = $_POST["checkout"];
//$room = $_POST["room"];


$result1 = mysql_query("select * from staff  where Staff_ID='$Staff_ID'") or die ("Err Can not to result") ;
$dbarr1 = mysql_fetch_array($result1) ;
			$Staff_User = $dbarr1["Staff_User"];


$result = mysql_query("select * from member  where Mem_ID='$AMem_ID'") or die ("Err Can not to result") ;
$dbarr = mysql_fetch_array($result) ;
			$Mem_ID = $dbarr["Mem_ID"];
$nDate = Date("Y-m-d");


$startD = explode("/",$checkin);
$endD = explode("/",$checkout);

if($endD[2] > $startD[2] ) 
{
		if($startD[1] == 12 && $endD[1] == 1 ) 
		{
			$sday = 31- $startD[0] ; 
			$eday =  $endD[0] ; 
			$Rns = $sday + $eday ;
		}
		else if($startD[1] == 11  && $endD[1] == 1) 
		{
			$sday = 30- $startD[0] ; 
			$eday =  $endD[0] ; 
			$nday = 31;
			
			$Rns = $sday + $eday + $nday;
		}
		else if($startD[1] == 10 && $endD[1] == 1) 
		{
			$sday = 31- $startD[0] ; 
			$eday =  $endD[0] ; 
			$nday = 30;
			$nday1 = 31;
			
			$Rns = $sday + $eday + $nday + $nday1 ;
		}
		else
		{  echo"Error"; exit();}
}

else // ปีเดียวกัน
{


			if($startD[1] == 1)
			$sday = 31;
		else if($startD[1] == 2)
			$sday = 28;
		else if($startD[1] == 3)
			$sday = 31;
		else if($startD[1] == 4)
			$sday = 30;
		else if($startD[1] == 5)
			$sday = 31;
		else if($startD[1] == 6)
			$sday = 30;
		else if($startD[1] == 7)
			$sday = 31;
		else if($startD[1] == 8)
			$sday = 31;
		else if($startD[1] == 9)
			$sday = 30;
		else if($startD[1] == 10)
			$sday = 31;
		else if($startD[1] == 11)
			$sday = 30;
		else 
			$sday = 31;
	
		$day1 = $sday - $startD[0] ;


			 if($endD[1] == $startD[1]) 
	{
			$Rns = $endD[0]-$startD[0] ;
	}
		else if($endD[1] - $startD[1]  == 2)
		{
			$nextM = $startD[1] +1;
		
			if($nextM[1] == 1)
				$sday = 31;
			else if($nextM[1] == 2)
				$sday = 28;
			else if($nextM[1] == 3)
				$sday = 31;
			else if($nextM[1] == 4)
				$sday = 30;
			else if($nextM[1] == 5)
				$sday = 31;
			else if($nextM[1] == 6)
				$sday = 30;
			else if($nextM[1] == 7)
				$sday = 31;
			else if($nextM[1] == 8)
				$sday = 31;
			else if($nextM[1] == 9)
				$sday = 30;
			else if($nextM[1] == 10)
				$sday = 31;
			else if($nextM[1] == 11)
				$sday = 30;
			else 
				$sday = 31;

			$Rns = $day1+$endD[0] +$sday ;
		}
		else if($endD[1] - $startD[1]  == 3) 
		{
			$nextM = $startD[1] +1;
			$nextM1 = $startD[1] +2;

			if($nextM[1] == 1)
				$sday = 31;
			else if($nextM[1] == 2)
				$sday = 28;
			else if($nextM[1] == 3)
				$sday = 31;
			else if($nextM[1] == 4)
				$sday = 30;
			else if($nextM[1] == 5)
				$sday = 31;
			else if($nextM[1] == 6)
				$sday = 30;
			else if($nextM[1] == 7)
				$sday = 31;
			else if($nextM[1] == 8)
				$sday = 31;
			else if($nextM[1] == 9)
				$sday = 30;
			else if($nextM[1] == 10)
				$sday = 31;
			else if($nextM[1] == 11)
				$sday = 30;
			else 
				$sday = 31;

			if($nextM1[1] == 1)
				$sday1 = 31;
			else if($nextM1[1] == 2)
				$sday1 = 28;
			else if($nextM1[1] == 3)
				$sday1 = 31;
			else if($nextM1[1] == 4)
				$sday1 = 30;
			else if($nextM1[1] == 5)
				$sday1 = 31;
			else if($nextM[1] == 6)
				$sday = 30;
			else if($nextM1[1] == 7)
				$sday1 = 31;
			else if($nextM1[1] == 8)
				$sday1 = 31;
			else if($nextM1[1] == 9)
				$sday1 = 30;
			else if($nextM1[1] == 10)
				$sday1 = 31;
			else if($nextM1[1] == 11)
				$sday1= 30;
			else 
				$sday1 = 31;

			$Rns = $day1+$endD[0] +$sday+$sday1 ;
		}
		else
		{  echo"Error"; exit();}
}

//echo"Rns = $Rns"; exit();

$chkinD = explode("/",$checkin);
$ChkDate = "$chkinD[2]-$chkinD[1]-$chkinD[0]";

$chkoutD = explode("/",$checkout);
$Chk_ODate = "$chkoutD[2]-$chkoutD[1]-$chkoutD[0]";

//echo"$ChkDate";exit();
if( $AMem_ID =="")
{
	$sql1 = "insert into reserve (Res_ID,Res_Date,Resort_ID,Res_CheckIn,Res_CheckOut,Res_NumRoom,Mem_ID,Staff_ID,Res_status) values('0','$nDate','$bookType','$ChkDate','$Chk_ODate','$Rns','$Mem_ID','$Staff_ID','2')";
	$result2 = mysql_db_query($dbname, $sql1);

	$sql2 = "update resort  set  Sta_ID ='3' where Resort_ID = '$bookType' ";
    $dbquery = mysql_db_query($dbname,$sql2);
}
else
{
	$sql1 = "insert into reserve (Res_ID,Res_Date,Resort_ID,Res_CheckIn,Res_CheckOut,Res_NumRoom,Mem_ID,Staff_ID,Res_status) values('0','$nDate','$bookType','$ChkDate','$Chk_ODate','$Rns','$Mem_ID','$Staff_ID','1')";
	$result2 = mysql_db_query($dbname, $sql1);

	$sql2 = "update resort  set  Sta_ID ='2' where Resort_ID = '$bookType' ";
  $dbquery = mysql_db_query($dbname,$sql2);
}



	if (!$result2)
		{ 	echo("เอ็กซิคิวต์คำสั่ง SQL ไม่ได้ " . mysql_error() ); exit;	}
	else
		{	
			echo "<font size=3>บันทึกข้อมูลเรียบร้อยแล้ว <br>";

	header("location:SReport.php?&login_true=$Staff_User");
	//	echo"top.location='booking.php' ";

		}		  

?>