#define SOLID "#"
#define EMPTY " "
#define WET   "v"

Dim Shared As String grid()
Dim Shared As Integer last, lastrow, m, n

Sub make_grid(x As Integer, y As Integer, p As Double)
    m = x
    n = y
    Redim Preserve grid(x*(y+1)+1)
    last = Len(grid)
    Dim As Integer lastrow = last-n
    Dim As Integer i, j

    For i = 0 To x-1
        For j = 1 To y
            grid(1+i*(y+1)+j) = Iif(Rnd < p, EMPTY, SOLID)
        Next j
    Next i
End Sub

Function ff(i As Integer) As Boolean
    If i <= 0 Or i >= last Or grid(i) <> EMPTY Then Return 0
    grid(i) = WET
    Return i >= lastrow Or (ff(i+m+1) Or ff(i+1) Or ff(i-1) Or ff(i-m-1))
End Function

Function percolate() As Integer
    For i As Integer = 2 To m+1
        If ff(i) Then Return 1
    Next i
    Return 0
End Function

Dim As Double p
Dim As Integer ip, i, cont

make_grid(15, 15, 0.55)
Print "15x15 grid:"
For i = 1 To Ubound(grid)
    Print grid(i);
    If i Mod 15 = 0 Then Print
Next i

Print !"\nrunning 10,000 tests for each case:"
For ip As Ubyte = 0 To 10
    p = ip / 10
    cont = 0
    For i = 1 To 10000
        make_grid(15, 15, p)
        cont += percolate()
    Next i
    Print Using "p=#.#:  #.####"; p; cont/10000
Next ip
Sleep