Can anyone tell me how to get started on this assignment?

The greatest common divisor of two positive intergers is the largest interger that divides the numbers exactly. We can write a recursive formula for finding the GCD, given that the two numbers are called a and b, as:

GCD[a, b] = a, if b = 0

GCD[a, b]= LCF[b, a%b], if b > 0

Implement this recursive formula as a recursive C++ function, and write a driver program that allows you to test it interactively.