The greatest common divisor (GCD) of two positive-integers is the largest integer that div...

The greatest common divisor (GCD) of two positive-integers is the largest integer that divides the numbers exactly. For example, the GCD of 14 and 21 is 7; for 13 and 22, it is 1; and for 45 and 27, it is 9. We can write a recursive formula for finding the GCD given that the two numbers are called a and b,as:

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