Adding and removing inventory based on form input

[Termy]

Hello,

TDLR; I need help with forms and user input to help me add and remove inventory depending on there input

I’m working on a inventory management app for the company i work for and I’ve hit a snag. How the app works currently is that there us a form that people fill out to add or remove inventory. Then after it logs the entry. In said form they had to select the item, date, and how much they are adding or removing. However, that last part is a bit weird, in order for a person to remove inventory they have to use negative numbers in the text box. I was wondering if there was a way to use kind of like an IF statement? What I mean is IF (Adding/Removing) = adding then it would add the amount that the user inputted into the amount column. The same goes for removing expect it subtracts from the inventory. Then in the log there it indicates which happened. Any help would be much help.