How can I count the unique numbers in an array without rearranging the array elements?

If you have .NET 3.5 you can easily achieve this with LINQ via:

int numberOfElements = myArray.Distinct().Count();

Non LINQ:

List<int> uniqueValues = new List<int>();
for(int i = 0; i < myArray.Length; ++i)
{
    if(!uniqueValues.Contains(myArray[i]))
        uniqueValues.Add(myArray[i]);
}
int numberOfElements = uniqueValues.Count;