' FB 1.05.0 Win64

Function Mean(array() As Double) As Double
  Dim length As Integer = Ubound(array) - Lbound(array) + 1
  If length = 0 Then
    Return 0.0/0.0 'NaN
  End If
  Dim As Double sum = 0.0
  For i As Integer = LBound(array) To UBound(array)
    sum += array(i)
  Next
  Return sum/length
End Function

Function IsNaN(number As Double) As Boolean
  Return Str(number) = "-1.#IND" ' NaN as a string in FB
End Function

Dim As Integer n, i
Dim As Double num
Print "Sample input and output"
Print
Do
  Input "How many numbers are to be input ? : ", n
Loop Until n > 0
Dim vector(1 To N) As Double
Print
For i = 1 to n
  Print "  Number #"; i; " : ";
  Input "", vector(i)
Next
Print
Print "Mean is"; Mean(vector())
Print
Erase vector
num = Mean(vector())
If IsNaN(num) Then
  Print "After clearing the vector, the mean is 'NaN'"
End If
Print
Print "Press any key to quit the program"
Sleep