I'm using a function in which I'm assigning a variable a tablename value like:
function mshirt(){
    var tbname='m_shirts';
}
Then in PHP form action section:
include 'database_connection.php';
$tablename=tbname;
if(isset($_POST['submit'])){
    $Size=$_POST['size'];
    $Color=$_POST['color'];
    $Code=$_POST['code'];
    $Brand=$_POST['brand'];
    $sql="INSERT INTO `$tablename` (size,color,code,brand) VALUES('$Size','$Color','$Code','$Brand')";
    if(mysqli_query($conn,$sql)){
        echo("Added Succesfully");
    }
    else 
        echo("Failed to Add");
The problem is that it assumes tbname to be undefined constant.
 
     
     
    