by Ryan Kwok (1 Submission)
Category: String Manipulation
Compatability: Visual Basic 3.0
Difficulty: Intermediate
Date Added: Wed 3rd February 2021
Rating: 
(2 Votes)
This is a recursive function to calculate a string formula. For example: You have a formula like "3*((2+6)*2-2)/(2+2)". You just call the function to get the answer. Hope this is useful to somebody:)
Inputs
sFormula - string
Code Returns
return the result of the formula
VBcodersPublic Function calc(sFormula As String) As Double
'This is a recursive function to calculate a valid
'math formula.
Dim sHead As String, sTail As String
Dim sTemp As String, lPos As Long
Dim cnt As Long, dblTemp As Double
Dim I As Long
cnt = 0
If InStr(sFormula, "(") > 0 Then
'calculate the string within bracket first
lPos = InStr(sFormula, "(")
For I = lPos + 1 To Len(sFormula)
If Mid(sFormula, I, 1) = "(" Then cnt = cnt + 1
If Mid(sFormula, I, 1) = ")" Then
If cnt = 0 Then Exit For
cnt = cnt - 1
End If
Next
sTemp = Mid(sFormula, lPos + 1, I - lPos - 1)
dblTemp = calc(sTemp)
sTemp = Replace(sFormula, "(" & sTemp & ")", CStr(dblTemp))
calc = calc(sTemp)
ElseIf InStr(sFormula, "+") > 0 Then
'Add
lPos = InStr(sFormula, "+")
sHead = Left(sFormula, lPos - 1)
sTail = Right(sFormula, Len(sFormula) - lPos)
calc = calc(sHead) + calc(sTail)
ElseIf InStr(sFormula, "-") > 0 Then
'Subtract
lPos = InStr(sFormula, "-")
sHead = Left(sFormula, lPos - 1)
sTail = Right(sFormula, Len(sFormula) - lPos)
calc = calc(sHead) - calc(sTail)
ElseIf InStr(sFormula, "*") > 0 Then
'Multiply
lPos = InStr(sFormula, "*")
sHead = Left(sFormula, lPos - 1)
sTail = Right(sFormula, Len(sFormula) - lPos)
calc = calc(sHead) * calc(sTail)
ElseIf InStr(sFormula, "/") > 0 Then
'Divide
lPos = InStr(sFormula, "/")
sHead = Left(sFormula, lPos - 1)
sTail = Right(sFormula, Len(sFormula) - lPos)
calc = calc(sHead) / calc(sTail)
Else
calc = CDbl(sFormula)
End If
End Function
