C# - Adding and Subtracting of Quantities/Stocks Connected to the Database (Point of Sale System)

Hello! Kumusta? Here's the tutorial for adding and subtracting quantities in my Point of Sale (POS) System example demo below.
Point of Sale (POS) System using C# and MySQL - • Point of Sale (POS) Sy...
Link for Mysql.Data.DLL - www.dll-files.com/mysql.data....
Here's the link to download MySql:
drive.google.com/file/d/1ej1P...
NOTE: For those who followed my tutorial, I forgot to close the connection in the `UpdateQuantityInDatabase` method on the last part.
Sorry about that, everyone! Please remember to add conn.Close(); or simply make sure to close your connection after using it. Thank you!