add rows with loop max value +1 - php

Question

I'm trying to add rows to the database based on the input value.
i.e. If input as "5", query will insert 5 rows to database. (this part is working fine)
Now, I need the bed_number to be +1 to the existing max(bed_number) but i can't seems to get it to work.
If existing max(bed_number) returns 5, than the query should add "6,7,8,9,10, etc" as the bed_number for the 5 entries.
If existing max(bed_number) returns null, than it should add "1,2,3,4,5, etc"
Right now, the result always return 1,2,3,4,5... regardless of the max count.
What i have here now is:
global $conn;
if ($values["number_of_bed"])
{
$add1 = $values["number_of_bed"]+1;
$existingBed = "select Max(bed_number) from bed where bed =" '".$i."'" +1;
for ($i=1;$i<$add1;$i++)
{
$strInsert = "insert into bed (unit_id,bed_number) values ('".$values["unit_id"]."','".$existingBed."')";
db_exec($strInsert,$conn);
}
header("Location: bed_list.php");
// Exit and Redirect to the list page after updating database
exit();

Answer 1

//echo "Number of customers: " . $data["c"];
global $conn;
if ($values["bed_number"])
{
$add1 = $values["bed_number"]+1;
//for ($i=1;$i<$values["bed_number"];$i++)
for ($i=1;$i<$add1;$i++)
{
$sql = "select max(bed_number) as c from bed where unit_id =" . $values["unit_id"];
$rs = CustomQuery($sql);
$data = db_fetch_array($rs);
$strInsert = "insert into bed (unit_id,bed_number) values ('".$values["unit_id"]."','".$data["c"]."'+1)";
// add more fields from the add page to be inserted into database
db_exec($strInsert,$conn);
}
header("Location: bed_list.php");
// Exit and Redirect to the list page after updating database
exit();
}