How many elements of array are not null?

Using LINQ you can try

int count = strArray.Count(x => x != null);

You can use Enumerable.Count:

string[] strArray = new string[50];
...
int result = strArray.Count(s => s != null);

This extension method iterates the array and counts the number of elements the specified predicate applies to.

Use LINQ:

int i = (from s in strArray where !string.IsNullOrEmpty(s) select s).Count();