String Equation Solver VB.NET

Module LHEquationSolver

    Function solveSingle(ByVal equ As String) 'solves equation without parenthesis such as "4-3*4-5/4*7-2+8*12".
        Dim fEqu As String = equ.Replace(" ", "")
        Dim chars As Char() = fEq*****Array()
        If (chars.Length > 0) Then
            While chars.Contains("+") Or chars.Contains("-") Or chars.Contains("*") Or chars.Contains("/")
                For I As Integer = 1 To chars.Length - 1 Step 1
                    Dim iChar As Char = chars(I)
                    If (iChar = "/" Or iChar = "*") Then

                        Dim subEquStart As Int32 = 0
                        Dim FirstNumber As Single = 0
                        Dim SecondNumber As Single = 0

                        For B As Integer = I - 1 To 0 Step -1 'before */
                            Dim bChar As Char = chars(B)
                            If (B = 0) Then
                                subEquStart = 0
                                FirstNumber = CSng(fEqu.Substring(0, I))
                                Exit For
                            ElseIf (bChar = "+" Or bChar = "-") Then
                                If (chars(B - 1) = "-" Or chars(B - 1) = "+") Then 'negative number check due to subtraction and negative both using "-".
                                    subEquStart = B
                                    FirstNumber = CSng(fEqu.Substring(B, I - B))
                                    Exit For
                                Else
                                    subEquStart = B + 1
                                    FirstNumber = CSng(fEqu.Substring(B + 1, I - B - 1))
                                    Exit For
                                End If
                            End If
                        Next

                        If (I + 2 > chars.Length - 1) Then
                            SecondNumber = CSng(fEqu.Substring(I + 1, chars.Length - I - 1))
                        Else
                            For A As Integer = I + 2 To chars.Length - 1 'after */
                                Dim aChar As Char = chars(A)
                                If (A = chars.Length - 1) Then
                                    SecondNumber = CSng(fEqu.Substring(I + 1, chars.Length - I - 1))
                                    Exit For
                                ElseIf (aChar = "+" Or aChar = "-" Or aChar = "*" Or aChar = "/") Then
                                    SecondNumber = CSng(fEqu.Substring(I + 1, A - I - 1))
                                    Exit For
                                End If
                            Next
                        End If

                        Dim wholeLength As Byte = (FirstNumber & iChar & SecondNumber).Length

                        Dim newEqu As String = ""
                        Select Case iChar
                            Case "*"
                                newEqu = fEqu.Substring(0, subEquStart) & (FirstNumber * SecondNumber) & fEqu.Substring(subEquStart + wholeLength)
                            Case "/"
                                newEqu = fEqu.Substring(0, subEquStart) & (FirstNumber / SecondNumber) & fEqu.Substring(subEquStart + wholeLength)
                        End Select

                        fEqu = newEqu
                        chars = fEq*****Array()
                        Exit For
                    ElseIf (chars.Contains("*") = False And chars.Contains("/") = False) Then

                        If (iChar = "+" Or iChar = "-") Then

                            Dim subEquStart As Int32 = 0
                            Dim FirstNumber As Single = 0
                            Dim SecondNumber As Single = 0

                            FirstNumber = CSng(fEqu.Substring(0, I))

                            If (I + 2 > chars.Length - 1) Then
                                SecondNumber = CSng(fEqu.Substring(I + 1, chars.Length - I - 1))
                            Else
                                For A As Integer = I + 2 To chars.Length - 1 'after */
                                    Dim aChar As Char = chars(A)
                                    If (A = chars.Length - 1) Then
                                        SecondNumber = CSng(fEqu.Substring(I + 1, chars.Length - I - 1))
                                        Exit For
                                    ElseIf (aChar = "+" Or aChar = "-") Then
                                        SecondNumber = CSng(fEqu.Substring(I + 1, A - I - 1))
                                        Exit For
                                    End If
                                Next
                            End If

                            Dim wholeLength As Byte = (FirstNumber & iChar & SecondNumber).Length
                            Dim newEqu As String = ""
                            Select Case iChar
                                Case "+"
                                    newEqu = fEqu.Substring(0, subEquStart) & (FirstNumber + SecondNumber) & fEqu.Substring(subEquStart + wholeLength)
                                Case "-"
                                    newEqu = fEqu.Substring(0, subEquStart) & (FirstNumber - SecondNumber) & fEqu.Substring(subEquStart + wholeLength)
                            End Select

                            fEqu = newEqu
                            chars = fEq*****Array()
                            Exit For
                        ElseIf (I = chars.Length - 1) Then
                            'equation done but still looping due to subtraction and negative both using "-". Didn't think about this when coming up with method.
                            Return CSng(fEqu)
                        End If
                    End If
                Next
            End While
            Return CSng(fEqu)
        End If
        Return 0
    End Function

    Function solveMulti(ByVal equ As String) As Single 'solves equation with parenthesis such as "3+2*5*(10+2-(14+2)/5*(99-12)/5)".
        Dim fEqu As String = equ.Replace(" ", "")
        Dim chars As Char() = fEq*****Array()
        If (chars.Length > 0) Then
            While chars.Contains("(")
                Dim pLefts As String() = fEqu.Split("(")
                Dim selectedEqu As String = pLefts(pLefts.Length - 1)
                Dim leftExcess As String = fEqu.Substring(0, fEqu.Length - selectedEqu.Length - 1)
                Dim subEquStart As Int32 = leftExcess.Length
                selectedEqu = selectedEqu.Split(")")(0)
                Dim rightExcess As String = fEqu.Substring(selectedEqu.Length + leftExcess.Length + 2)
                Dim result As Single = solveSingle(selectedEqu)
                Dim newEqu As String = leftExcess & result & rightExcess

                fEqu = newEqu
                chars = fEq*****Array()
            End While
            Return solveSingle(fEqu)
        End If
        Return 0
    End Function

    Sub Main()
        Console.WriteLine("-5*-4*-3*-2*-1 = " & solveMulti("-5*-4*-3*-2*-1"))
        Console.WriteLine("(1*1*-1)-5 = " & solveMulti("(1*1*-1)-5"))
        Console.WriteLine("3+2*5*(10+2-(14+2)/5*(99-12)/5) = " & solveMulti("3+2*5*(10+2-(14+2)/5*(99-12)/5)"))
        Console.WriteLine("4-3*4-5/4*7-2+8*12 = " & solveMulti("4-3*4-5/4*7-2+8*12"))
        Console.ReadKey()
    End Sub
End Module