Here is a program demonstrating how to get the names of the top-level subdirectories in a given directory:

C# get number of top-level subdirectories in a directory.

Here's a brief program that demonstrates counting the number of top-level subdirectories that reside within a given directory:

https://gist.github.com/kyrathasoft/1dc1a1eb4d6a2a56827dcb5f43840afe