Logic for a very simple booking script

[6pandn21]

Hello guys,
I am trying to make a very simple booking system. The booking will be either for the current or the next year only. There are three fields; number of person, type of meal and date. In any particualr day and meal, the number of person can't exceed 100. When the user enters a date, number of people and meal type, the bookingcheck script should check if the booking is available. If it is available; it will allow the user to make a booking for that day and meal type. If there was no booking placed on that day, the script should insert the booking details. My problem is in the logic details, I am being unable to lay out the logic for this. If anyone could clarify, I would be grateful. Thank you.

6pand21

<?php
		$a = mysql_real_escape_string ($_POST['guest_number']);
		$b = mysql_real_escape_string ($_POST['date']);
		$c = mysql_real_escape_string ($_POST['food_type']);
		$exploded = explode("/", $b);
		$d = $exploded[0];
		$e = $exploded[1];
		$f = $exploded[2];
		$year= date ("Y");
		$nextyear= $year + 1;
		if (($f != $year) and ($f != $nextyear))
		{
		echo"cannot book for this year";
		}
		else
		{
		$result=mysql_query("SELECT * FROM booking WHERE year ='$f' AND food_type ='$c'");
		
		while ($row= mysql_fetch_array($result))
		{
			$guest = $row['guest_number'] + $a;
			if ($guest > 100)
			{
			//number of guest error
			}
			else
			{
			// continue with the booking
			}
		}
		}
			
?>