Type GameState
    digitos(3) As Double
    operaciones(2) As String
End Type

Function randomDigits() As String
    Dim As String resultado = ""
    For i As Integer = 0 To 3
        resultado &= Str(Int(Rnd * 9) + 1)
    Next
    Return resultado
End Function

Function evaluate(digitos() As Double, operaciones() As String) As Double
    Dim As Double valor = digitos(0)

    For i As Integer = 0 To 2
        Select Case operaciones(i)
			Case "+": valor += digitos(i +1)
			Case "-": valor -= digitos(i +1)
			Case "*": valor *= digitos(i +1)
			Case "/": If digitos(i +1) <> 0 Then valor /= digitos(i +1)
        End Select
    Next

    Return valor
End Function

Sub permute(digitos() As Double, soluciones() As GameState, Byref solutionCnt As Integer, k As Integer)
    Dim As String*1 opChars(3) = {"+", "-", "*", "/"}
    Dim As String ops(2)
    Dim As Integer i, j, l, m

    If k = 4 Then
        For i = 0 To 3
            ops(0) = opChars(i)
            For j = 0 To 3
                ops(1) = opChars(j)
                For l = 0 To 3
                    ops(2) = opChars(l)
                    If Abs(evaluate(digitos(), ops()) - 24) < 0.001 Then
                        With soluciones(solutionCnt)
                            For m = 0 To 3: .digitos(m) = digitos(m): Next
                            For m = 0 To 2: .operaciones(m) = ops(m): Next
                        End With
                        solutionCnt += 1
                        Exit For 'Stop after first solution
                    End If
                Next
                If solutionCnt Then Exit For
            Next
            If solutionCnt Then Exit For
        Next
    Else
        For i = k To 3
            Swap digitos(i), digitos(k)
            permute(digitos(), soluciones(), solutionCnt, k +1)
            If solutionCnt Then Exit For
            Swap digitos(k), digitos(i)
        Next
    End If
End Sub

' Main program
Randomize Timer
Dim As Integer i
Dim As String cmd
Dim As Double digitos(3)
Dim As String operaciones(2)

Do
    Cls
    Print "24 Game"
    Print "Generating 4 digitos..."

    Dim As String inputDigits = randomDigits()
    Print "Make 24 using these digitos: ";
    For i = 1 To Len(inputDigits)
        Print Mid(inputDigits, i, 1); " ";
    Next
    Print

    Line Input "Enter your expression (e.g. 4+5*3-2): ", cmd

    Dim As Integer digitCnt = 0, opCnt = 0
    ' Parse user input
    For i = 1 To Len(cmd)
        Select Case Mid(cmd, i, 1)
        Case "1" To "9"
            digitos(digitCnt) = Val(Mid(cmd, i, 1))
            digitCnt += 1
        Case "+", "-", "*", "/"
            operaciones(opCnt) = Mid(cmd, i, 1)
            opCnt += 1
        End Select
    Next

    Dim As Double resultado = evaluate(digitos(), operaciones())
    Print "Your resultado: "; resultado

    If Abs(resultado - 24) < 0.001 Then
        Print !"\nCongratulations, you found a solution!"
    Else
        Print !"\nThe valor of your expression is "; resultado; " instead of 24!"

        Dim As GameState soluciones(1000)
        Dim As Integer solucCnt = 0

        permute(digitos(), soluciones(), solucCnt, 0)

        If solucCnt > 0 Then
            Print !"\nA possible solution could have been: ";
            With soluciones(0)
                Print .digitos(0) & .operaciones(0) & .digitos(1) & .operaciones(1) & .digitos(2) & .operaciones(2) & .digitos(3)
            End With
        Else
            Print !"\nThere was no known solution for these digitos."
        End If
    End If

    Print !"\nDo you want to try again? (press N for exit, other key to continue)"
Loop Until (Ucase(Input(1)) = "N")

Sleep