How to add listing fee without hardcoded

Hi guys, i used this line of code to ask for listingprice fee from anyone who list NFT on my MarketPlace, but it shows its hardcode with the following code below.

uint256 listingPrice = 0.1 ether;

So what i want exactly is to not hardcoded the listingPrice to 0.1 ether, all i want is to make it changeable whenever i want to change the listingPrice.

How do i do that?

I guess that you could make a function that can set that variable