Doors

Sub doors()

''''expected vs actual result: http://i.imgur.com/uEA2AZj.png
''''run as a VBA Macro in Excel

Dim dCount As Long 'door count
Dim car As Long 'used to randomly pick which door has the car
Dim choice As Long 'used to pick which door the contestant picks

Dim itr As Long 'number of iterations

Dim wins As Double 'number of wins

itr = 100000
dCount = 3

wins = 0

For i = 1 To itr

    'rnd double between 0 and 1, * door count, add 0.5 to account for rounding.
    car = Round((Math.Rnd * dCount) + 0.5, 0)
    choice = Round((Math.Rnd * dCount) + 0.5, 0)


    'If the door you picked "choice" is not the car,
    'then the host has shown that the remaining door *is* the car.
    'Therefore, by switching you win.
    If car <> choice Then
        wins = wins + 1 'increase wins
    End If


    'if the door you picked "choice" is the car,
    'then by switching you will lose.
    'Nothing done since winrate is not increased.

Next i

MsgBox "Expected: " & Round((dCount - 1) / dCount * 100, 2) & "%" _
& vbNewLine & "Actual: " & Round(wins / itr * 100, 2) & "%"

End Sub