GCD - subprogram w/o GCD built in Function

My task is to make a sub program to calculate the greatest common divisor (factor) between two numbers. Here is my code thus far:

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This is where I am getting stuck. I am familiar with the Euclidean Algorithm needed for this problem. However, I am not sure if I am using the Mod function correctly. Also, I do not know how to loop this back for the algorithm to work. I need for the new dividend to be (b*quotient) and for the divisor to be (Mod b*quotient). For extremely large nnumbers, this could get tedious. I need this code to work for any two numbers.

I only know the basic looping

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etc.

How do I loop such an algorithm without doing it number by number?

Another way:

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wouldn't this be using the built in function? What exactly is the ByVal in front of the variables?
So, in order for this sub program to work, I would need a separate function program to call back into the sub program?

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wouldn't this be using the built in function?

No, it's a stand-alone function.

What exactly is the ByVal in front of the variables?

It causes the function to receive a copy of the argument, rather than a pointer, which allows it to modify the arguments without modifying the variables passed by the calling routine.

So, in order for this sub program to work, I would need a separate function program to call back into the sub program?

It's a function; pass it two numbers, and it returns the GCD. It can be called from a worksheet or other VBA code.

Please take a few minutes to read the forum rules about CODE tags and quoting entire posts.

So, in order for this sub program to work, I would need a separate function program to call back into the sub program?

What shg is using is a strategy called recursion http://en.wikipedia.org/wiki/Recursive_algorithm and it is a common strategy in computing -- especially if the "bigger" problem can be broken down into smaller problems that look just like the bigger problem.

Here's another recursion example for calculating factorials. http://msdn.microsoft.com/en-us/libr...ice.12%29.aspx