updated final php code

<?php
echo "<body style='background-color:white'>";
$servername = "localhost";
$username = "root";
$password = "";
$dbname = "projectbus1";

$conn = mysqli_connect("localhost","root","","projectbus1");
// Check connection
if ($conn->connect_error) {
    
    die("Connection failed: " . $conn->connect_error);
} 
if ((isset($_POST['submit'])))
{     echo"<br>";echo"<br>";echo"<br>";echo"<br>";echo"<br>";echo"<br>";
        echo "<p align=center>WELCOME TO KL_RTC</p>"; 
        //echo "<br>";
        $presentlocation = $_POST['presentlocation'];
  $destination = $_POST['destination'];
  if($presentlocation==1)
    {echo "<p align=center>Present location-VIJAYAWADA </p>";}
  elseif($presentlocation==2) 
  {echo "<p align=center>Present location-TADEPALLI </p>";}
  elseif($presentlocation==3)
  {echo "<p align=center>Present location-PATHURRU</p>";}
  elseif($presentlocation==4)
  {echo "<p align=center>Present location-MANGALAGIRI</p>";}
  elseif($presentlocation==5)
  {echo "<p align=center>Present location-GUNTUR</p>";}

    //echo " To ";

  if($destination==1)
  {echo "<p align=center>Destination-VIJAYAWADA</p>";}
elseif($destination==2) 
{echo "<p align=center>Destination-TADEPALLI</p>";}
elseif($destination==3)
{echo "<p align=center>Destination-PATHURRU</p>";}
elseif($destination==4)
{echo "<p align=center>Destination-MANGALAGIRI</p>";}
elseif($destination==5)
{echo "<p align=center>Destination-GUNTUR</p>";}   
  //echo "<br>";

  $sqlwselect = "SELECT * FROM `destination` WHERE `destination`.`destination` <= $presentlocation ";
  $resultselect= mysqli_query($conn,$sqlwselect);
  while($roww = mysqli_fetch_array($resultselect))
  {
    $seatselect= $roww['seatnum'];
    //echo " seattt.....$seatselect";
    $sqlselect = "INSERT INTO assignseat(Seatnum) VALUES('$seatselect')";
    $resultinsert=mysqli_query($conn,$sqlselect);
  }
$sqlw = "DELETE FROM `destination` WHERE `destination`.`destination` <= $presentlocation ";
$resu=mysqli_query($conn,$sqlw);
$sqlwdeleting = "DELETE FROM `deleting` WHERE `deleting`.`destination` <= $presentlocation ";
$resu=mysqli_query($conn,$sqlwdeleting);

$count="SELECT * FROM destination";
$resulttt=mysqli_query($conn,$count);
$num_row=mysqli_num_rows($resulttt);
 //for deletetable....
 $countdelete="SELECT * FROM deleting";
 $resultdeleting=mysqli_query($conn,$countdelete);
  $num_row_delete=mysqli_num_rows($resultdeleting); 
  $num_rows=$num_row+$num_row_delete+1;   
 echo "<p align=center>Total no of passengers-$num_rows</p>"; 
 //echo "Total no of passengers-$num_rows \n";
 //echo "<br>";
 if($num_rows<"40")
 {
 echo "<p align=center>seats are available</p>"; 
 //{echo "seats are available";
 //echo "<br>";
}
 else
 {
 echo "<p align=center>seats are not available</p>"; 
 //{echo "seats are not available";
 //echo "<br>";
}
 
 $sqlww = "SELECT MAX(seatnum) as max_seatnum FROM destination";
 $resultt=mysqli_query($conn,$sqlww);
 if (!$resultt) {
  printf("Error: %s\n", mysqli_error($conn));
  exit();
}
	$row=mysqli_fetch_array($resultt);
//$seatno=$row['S.No'];
//$destination=$row['destination'];
//printf("%d\n",$row[0]"."<br>";
//echo "pav";
$seat=$row['max_seatnum'];


$seat=$seat+1;


if($num_rows<"40")

{
  $countt="SELECT * FROM assignseat";
  $resultttt=mysqli_query($conn,$countt);
  //echo "value2-$resulttt";
  $num_roww=mysqli_num_rows($resultttt);
  $num_rowsinassign=$num_roww; 
  //echo "noofemptyseats=$num_rowsinassign";   
 if($num_rowsinassign > "0")
 {
  $sqlassign="SELECT MIN(Seatnum) as min_seatnum FROM assignseat";
  $resultassign=mysqli_query($conn,$sqlassign);
  if (!$resultassign) {
    printf("Error: %s\n", mysqli_error($conn));
    exit();
  }
  $rowassign=mysqli_fetch_array($resultassign);
  $seat=$rowassign['min_seatnum'];
  echo "<p align=center>Seatnum-$seat</p>";
  $sqlassigndelete="DELETE FROM `assignseat` WHERE Seatnum IN (select min(Seatnum) from `assignseat`)";
  $resultassigndelete=mysqli_query($conn,$sqlassigndelete);
 }
 else
 {
   echo "<p align=center>seatnum-$seat</p>";
 }
 // echo "need to add more code";
  /**for($abc=1;$abc<=40;$abc++)
  {
  $sqlquery="SELECT  * FROM destination where 'destination'.'seatnum'=$abc";
  $sqlresult=mysqli_query($conn,$sqlquery);
 // $roww=mysqli_fetch_array($sqlresult);
  //$seatfor=$roww['seatnum'];
  echo "forloop-$sqlresult";
  echo "<br>";

  if(!$sqlresult) 
  {
    echo "seatnuminside-$abc";
    $seat=$abc;
    printf("Error: %s\n", mysqli_error($conn));
    //exit();
    break;
  }*/
 // }
  //echo "<br>";
}
else if($num_rows>="40")
{
  //$sqlelseif="SELECT * FROM destination WHERE destination < '$destination' ";
  $sqlelseif="SELECT * FROM destination WHERE destination < '$destination' ";
  $resultif=mysqli_query($conn,$sqlelseif);
  while($rowgreater=mysqli_fetch_array($resultif))
  {
    $greaterdestination=$rowgreater['destination'];
    $greater="INSERT INTO greater('destination') values ('$greaterdestination')";
    $sqlgreatercon=mysqli_query($conn,$greater);
  }
  $greaterrows=mysqli_num_rows($resultif);
  //echo "....$greaterrows.....";
  if (!$resultif) 
  {
    echo "no lesser destination available";
    printf("Error: %s\n", mysqli_error($conn));
    exit();
  }
  if($greaterrows== 0)
  {
    $seat=0;
   // echo "no lesser destination available";
  }
  else
  {
  $resultif=mysqli_query($conn,$sqlelseif);
  while($row  = mysqli_fetch_array($resultif))

  {
   // echo "helloo";
    $presentatdestination = $row['present'];
    $destinationatdestination = $row['destination'];
    $seatatdestination = $row['seatnum'];
  }
 // echo "presentvaluees-$presentatdestination";
  //echo "destinationvalues-$destinationatdestination";
  //echo "seatvaluees-$seatatdestination";
  $sql = "INSERT INTO deleting (present,destination,seatnum) VALUES('$presentatdestination','$destinationatdestination','$seatatdestination')";
  $result=mysqli_query($conn,$sql);
  if (!$result) 
  {
    printf("Error: %s\n", mysqli_error($conn));
    exit();
  }
  
  $sqlwgreater = "DELETE FROM `destination` WHERE `destination`.`seatnum` = $seatatdestination ";
  $resu=mysqli_query($conn,$sqlwgreater);
  echo "<p align=center>seat-$seatatdestination at destination-$destinationatdestination</p>";
  echo "<br>";
  $seat=$seatatdestination;
  }
}  
  

/*  echo "testing-$resultif";
  if (!$resultif) {
    printf("Error: %s\n", mysqli_error($conn));
    exit();
  }
  $rowif=mysqli_fetch_array($resultif);
  $seat=$rowif['seatnum'];
  $comingplace=$rowif['destination'];
  echo "seatnumelseif-$seat"."at-$comingplace";
  echo "<br>";
}
else
{
  echo "seatnum=$seat";
  echo "<br>";
}*/

$sql = "INSERT INTO destination (present,destination,seatnum) VALUES('$presentlocation','$destination','$seat')";
  $result=mysqli_query($conn,$sql);
  if (!$result) {
    printf("Error: %s\n", mysqli_error($conn));
    exit();
  }
  $sql = "INSERT INTO temp (present,destination,seatnum) VALUES('$presentlocation','$destination','$seat')";
  $result=mysqli_query($conn,$sql);
  if (!$result) 
  {
    printf("Error: %s\n", mysqli_error($conn));
    exit();
  }
echo "<p align=center>THANKS FOR USING KL_RTC</p>";
  //echo "value2-$result"."<br>";
  //$x++;
     
      
      // $Seatnum=110178;
        //$sql = "INSERT INTO seatnumt (Seatnum) VALUES('$Seatnum')";
        //$result=mysqli_query($conn,$sql);
        //echo "hlooo";
}

/*if ($conn->query($sql) === TRUE) {
  header('Location: retrive.php');
} else {
    echo "Error: " . $sql . "<br>" . $conn->error;

}*/
?>