# Add Minus Price to User Credit

Hello all,

People who can buy something from me have a customer account with a “credit”. It is normal that this field is in the minus. So a drink that costs 1,70€ must be booked as minus. So the “credit” should be -1,70€. How can I change the sign when booking the item?

With the button “book” I have a change in the current user. First I get the current “credit” “Current Users’s credit” and book to it the articles he has ordered “Calculate SumProduct”.

Thank you

Multiply the expression with - 1

Do you have an example? I don’t now how it works. Thank you

Calculate Sum product * -1

Actually why aren’t you just doing credit = Current user’s credit - Calculate Sum product? That’s logically equivalent to Current user’s credit + Calculate Sum product * -1

The credit could be a positive or negativ value. That’s the reason why

But you’re calculating this sum product on a shopping cart… surely that’s always positive as products can’t have a negative value?

Then Current user’s credits - Cart’s sum product is always correct.