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- sub something_click()
- textbox2.text=eval(textbox1.text)
- end sub
1. Create 2 string arrays, and save numbers in one and operators in the other one:
2. Transform the first array into a doubles array (so you can work using Option Strict)
3. Evaluate powers (i dont evaluate roots, since you can use a^0.5 instead of sqrt, etc...)
4. Evaluate products and divisions.
5. Evaluate sum and difference.
After this little function is done, i like to make another function to handle parenthesis, using some recursivity, this is very useful while working with roots, since you can write a^(1/5) instead of the 5th root.
Lets call the first function 'Basics', and lets call the parenthesis handler 'Eval', and they could look like this:
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- Public Function Basics(ByVal Str1 As String) As Double
- Dim i, j, k As Integer
- Dim Boo1 As Boolean = False
- Dim mStr1(1), mStr2(0), mStr3(0), mStr4(0) As String
- Dim mDou1(), mDou2(), mDou3() As Double
- If Str1 = "" Then Return 0 : Exit Function
- '----------------------------------------------------------'
- ' Save in mStr1 the numbers. Save in mStr2 the operators. '
- '----------------------------------------------------------'
- j = 1
- For i = 1 To Str1.Length
- k = Asc(Mid(Str1, i, 1))
- If (k >= Asc("0") And k <= Asc("9")) Or k = Asc(".") Or (k = Asc("-") And Boo1 = False) Then
- mStr1(j) = mStr1(j) & Chr(k): Boo1 = True
- ElseIf k = 69 Then
- mStr1(j) = mStr1(j) & Chr(69) & Mid(Str1, i + 1, 1): i = i + 1
- Else
- If Boo1 = True Then
- ReDim Preserve mStr2(j)
- mStr2(j) = Chr(k): j = j + 1
- ReDim Preserve mStr1(j)
- End If
- Boo1 = False
- End If
- Next
- '--------------------------------------'
- ' Save in mDou1 the numbers as doubles '
- '--------------------------------------'
- ReDim mDou1(UBound(mStr1))
- For i = 1 To UBound(mStr1): mDou1(i) = CDbl(mStr1(i)): Next
- '------------------------'
- ' First priority: powers '
- '------------------------'
- j = 1: ReDim mDou2(1): mDou2(1) = mDou1(1)
- For i = 1 To UBound(mStr2)
- If mStr2(i) = "^" Then: mDou2(j) = mDou2(j) ^ mDou1(i + 1)
- Else
- ReDim Preserve mStr3(j): mStr3(j) = mStr2(i)
- j = j + 1: ReDim Preserve mDou2(j)
- mDou2(j) = mDou1(i + 1)
- End If
- Next
- If UBound(mStr3) = 0 Then Return mDou2(1) : Exit Function
- '-----------------------------------------'
- ' Second priority: products and quotients '
- '-----------------------------------------'
- j = 1: ReDim mDou3(1): mDou3(1) = mDou2(1)
- For i = 1 To UBound(mStr3)
- If mStr3(i) = "*" Then: mDou3(j) = mDou3(j) * mDou2(i + 1)
- ElseIf mStr3(i) = "/" Then: mDou3(j) = mDou3(j) / mDou2(i + 1)
- Else
- ReDim Preserve mStr4(j): mStr4(j) = mStr3(i)
- j = j + 1: ReDim Preserve mDou3(j)
- mDou3(j) = mDou2(i + 1)
- End If
- Next
- If UBound(mStr4) = 0 Then Return mDou3(1) : Exit Function
- '---------------------------------------'
- ' Third priority: sums and differences. '
- '---------------------------------------'
- Basics = mDou3(1)
- For i = 1 To UBound(mStr4)
- If mStr4(i) = "+" Then: Basics = Basics + mDou3(i + 1)
- ElseIf mStr4(i) = "-" Then: Basics = Basics - mDou3(i + 1): End If
- Next
- End Function
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- Public Function Eval(ByVal Str1 As String) As Double
- Dim i, j, k(2), c As Integer
- Dim Str2 As String
- If Str1 = "" Then Return 0 : Exit Function
- '------------------------------'
- ' Find the outern parenthesis. '
- '------------------------------'
- j = 0
- For i = 1 To Str1.Length
- If Mid(Str1, i, 1) = "(" Then
- If j = 0 Then k(1) = i
- j = j + 1
- ElseIf Mid(Str1, i, 1) = ")" Then
- If j = 1 Then: k(2) = i: Exit For: End If
- j = j - 1
- End If
- Next
- '----------------------------------------------------------------------'
- ' Using recursivity, it'll find the inner ones, and add '*' when needed'
- '----------------------------------------------------------------------'
- If j = 1 Then
- If k(1) > 1 Then c = Asc(Mid(Str1, k(1) - 1, 1))
- Str2 = ""
- If (c >= Asc("0") And c <= Asc("9")) Or c = Asc(".") Then Str2 = "*"
- If c = Asc("-") Then Str2 = "1*"
- Str1 = Eval(Mid(Str1, 1, k(1) - 1) & Str2 & Eval(Mid(Str1, k(1) + 1, k(2) - k(1) - 1)).tostring & Mid(Str1, k(2) + 1).tostring).tostring
- End If
- Return basics(Str1)
- End Function
You should also note that it will add a '*' when a parenthesis needs it before, but it won't when it needs it after. so 2(8) = 16 but (2)8 will be an error.
It's quite a simple function, but im sure you can find it useful.
Kad
