If you find yourself in a situation where you need to pass a lot of data around, a struct is great. Consider information about a book. You could group it into a struct that describes it and pass it around.
Consider a book-keeping system. You might want a structure that contains relevant information about a specific individual or whatever the system is book-keeping.
Basically, they are classes without member functions.
Ah ok! Well, seeing as the only function of the actual function is passing 2 numbers, I don't think using a structure will be necessary.