How to calculate fee when dealing with different decimals token?

Question

I'm kinda struggling here to find a solution.

I have a code where user can deposit token like USDC, DAI etc...

For example USDC had 6 decimals and DAI has 18 decimals.

How can I have a generic fee calculation in my function so it handle all different case when decimals are differents and also avoid rounding by 0 ?

I have something like this for the calculation :

uint256 feeToCollect = (amount * feeBps * 10**18) / BPS; 

uint256 amountWithFee = amount + fee; 

IERC20(token).transferFrom(msg.sender, address(this), amountWithFee;

amount = amount that the user deposit

feeBps = 10 so it's 0.1%

BPS = 10000

10**18 is a scale to avoid rounding by 0.

Thank you for your help !

Answer 1

If I understand the math problem correctly, the code should look something like that:

uint decimalFactor = IERC20(token).decimals(); //should return 18 or 6 in your case.

uint256 feeToCollect = (amount * feeBps * 10**decimalFactor) / BPS;