Answer: Copyright law
Copyright is security for tangible aspects of an idea. It is intended to give the creator of something original the ability to use and make money from it, without others being able to use it themselves. There are a number of limitations that do allow for a widespread use, they protect the derivatives of an idea also called intellectual property. Copyright tends to cover literary and artistic work e.g. books, movies. To get a better idea copyright is the reason you just can’t print and sell harry potter books or download pirated movies
Since the "price profit" app is an idea it is protected by the copyright law.
