If I understand you want to do something like:
public double AverageOf10(double[10] array)
{
}
and have this:
double[] values = new double[11]{1,2,3,4,5,6,7,8,9,10,11};
double avg = AverageOf10(values);
give a compile time error. (Edit: or even a run time error, but do it automatically.)
If that's what you want, you can't do that.
The best you can do would be to explicitly check the length of the passed array within the method at run-time:
public double AverageOf10(double[] array)
{
if (array == null)
throw new ArgumentNullException("array");
if (array.Length != 10)
throw new ArgumentException("array is incorrect length", "array");
}