The advice above is accurate, Have done it many times (Have 2 scanners on my phone) one is RED LASER which has some neat features, Many will let you generate your own QR codes by the way,, you can encode name, address, telephone and web page and then save the code, copy it to a business card printer (Avery Label Pro limited) and print it out on cards.
However, To get both the scanner *AND* Gas Buddy apps.
Go to the Play Store
in the search box enter first: Gas Buddy and press on the magnifying glass.
Then once that one is started go back to the search window and enter QR CODE
You should be rewarded again.