C++--Help with a for loop

I'm working on a multifile program (header, definitions, driver, etc) encapsulates three banking rates: a Fed rate, a Prime rate, and a Lending rate. I want to increment each rate by a fixed ratio, so that if for example the Fed rate is at 6 percent, the Prime rate increases by 2 points to 8 percent, and the Lending rate increases by 3 points above the Prime rate to 11 percent. I want to use a for loop in a function. Looking for suggestions on what the loop and function might look like.