Source code in the freebasic programming language

#define MAX(a, b) iif((a) > (b), (a), (b))
Dim Shared As Integer pow, signo
Dim Shared As String t
t = "-0+"

Function deci(cadena As String) As Integer
    Dim As Integer i, deci1
    Dim As String c1S
    pow = 1
    For i = Len(cadena) To 1 Step -1
        c1S = Mid(cadena,i,1)
        signo = Instr(t, c1S)-2
        deci1 = deci1 + pow * signo
        pow *= 3
    Next i
    Return deci1
End Function

Function ternary(n As Integer) As String
    Dim As String ternario
    Dim As Integer i, k
    While Abs(n) > 3^k/2
        k += 1
    Wend
    k -= 1
    
    pow = 3^k
    For i = k To 0 Step -1
        signo = (n>0) - (n<0)
        signo *= (Abs(n) > pow/2)
        ternario += Mid(t,signo+2,1)
        n -= signo*pow
        pow /= 3
    Next
    If ternario = "" Then ternario = "0"
    Return ternario
End Function

Function negate(cadena As String) As String
    Dim As String negar = ""
    For i As Integer = 1 To Len(cadena)
        negar += Mid(t, 4-Instr(t, Mid(cadena,i,1)), 1)
    Next i
    Return negar
End Function

Function pad(cadenaA As String, n As Integer) As String  
    Dim As String relleno = cadenaA
    While Len(relleno) < n
        relleno = "0" + relleno
    Wend
    Return relleno
End Function

Function addTernary(cadenaA As String, cadenaB As String) As String
    Dim As Integer l = max(Len(cadenaA), Len(cadenaB))
    Dim As Integer i, x, y, z
    cadenaA = pad(cadenaA, l)
    cadenaB = pad(cadenaB, l)
    Dim As String resultado = ""
    Dim As Byte llevar = 0
    For i = l To 1 Step -1
        x = Instr(t, Mid(cadenaA,i,1))-2
        y = Instr(t, Mid(cadenaB,i,1))-2
        z = x + y + llevar
        
        If Abs(z) < 2 Then
            llevar = 0
        Elseif z > 0 Then
            llevar = 1: z -= 3
        Elseif z < 0 Then
            llevar = -1: z += 3
        End If
        
        resultado = Mid(t,z+2,1) + resultado
    Next i
    If llevar <> 0 Then resultado = Mid(t,llevar+2,1) + resultado

    i = 0
    While Mid(resultado,i+1,1) = "0"
        i += 1
    Wend
    resultado = Mid(resultado,i+1)
    If resultado = "" Then resultado = "0"
    Return resultado
End Function

Function subTernary(cadenaA As String, cadenaB As String) As String
    Return addTernary(cadenaA, negate(cadenaB))
End Function

Function multTernary(cadenaA As String, cadenaB As String) As String
    Dim As String resultado = ""
    Dim As String tS = "", cambio = ""
    For i As Integer = Len(cadenaA) To 1 Step -1
        Select Case Mid(cadenaA,i,1)
        Case "+": tS = cadenaB
        Case "0": tS = "0"
        Case "-": tS = negate(cadenaB)
        End Select
        
        resultado = addTernary(resultado, tS + cambio)
        cambio += "0"
    Next i
    Return resultado
End Function


Dim As String cadenaA = "+-0++0+"
Dim As Integer a = deci(cadenaA)
Print "      a:", a, cadenaA 

Dim As Integer b = -436
Dim As String cadenaB = ternary(b)
Print "      b:", b, cadenaB

Dim As String cadenaC = "+-++-"
Dim As Integer c = deci(cadenaC)
Print "      c:", c, cadenaC

'calcular en ternario
Dim As String resS = multTernary(cadenaA, subTernary(cadenaB, cadenaC))
Print "a*(b-c):", deci(resS), resS

Print !"\nComprobamos:"
Print "a*(b-c): ", a * (b - c)
Sleep