Dim result As Double
Dim plus As String()
Dim Substract As String()
Dim multiply As String()
Dim divide As String()
Dim powerto As String()
Dim num As Long
If TextBox1.Text.Contains("^") Then
powerto = TextBox1.Text.Split("^")
For Each NumToPower As String In powerto
result = System.Math.Pow(NumToPower, powerto.Length)
' num ^= CStr(NumToPower)
Next
End If
If TextBox1.Text.Contains("/") Then
divide = TextBox1.Text.Split("/")
For Each numbertodivide As String In divide
If numbertodivide <> 0 Then
num /= CStr(numbertodivide)
result = num
Else
MessageBox.Show("Cannot Divide By 0")
Exit Sub
End If
Next
End If
If TextBox1.Text.Contains("*") Then
multiply = TextBox1.Text.Split("*")
For Each NumToPower As String In multiply
num *= CStr(NumToPower)
Next
result = num
End If
If TextBox1.Text.Contains("+") Then
plus = TextBox1.Text.Split("+")
For Each NumToPower As String In plus
num += CStr(NumToPower)
Next
result = num
End If
If TextBox1.Text.Contains("-") Then
Substract = TextBox1.Text.Split("-")
For Each NumToPower As String In Substract
num -= CStr(NumToPower)
Next
result = num
End If
MessageBox.Show(result)
我有一个TextBox，并在其中编写例如＆＃34; 15 * 2 ^ 3＆＃34;在计算之前，我怎样才能得到这个等式中的每个数字？
答案 0 :(得分：0)
Dim input As String = "15*2^35"
Dim digits() As String = Regex.Split(input, "[^0-9]+")
For Each item As String In digits
Console.WriteLine(item)
Next
但在你的情况下，最好实现tokenizer
您的案例的完整语法是
<exp> ::= <exp> + <term> | <exp> - <term> | <term>
<term> ::= <term> * <power> | <term> / <power> | <power>
<power> ::= <factor> ^ <power> | <factor>
<factor> ::= ( <exp> ) | <int>
<int> ::= <digit> <int> | <digit>
<digit> ::= 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9
对于简单的方程式" +-*/ and ( ) "，您可以尝试我简单的天真解决方案。请注意，我不擅长解析器或语法因此我使用了简单的就绪语法并删除了左递归。
Simple arithmetic grammar, with left recursion removed, is
expression → factor E’
E’ → + factor E’ | - factor E’ | ε
factor → term F’
F’ → * term F’ | / term F’ | ε
term → digit | ( expression )
digit → 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9
以下是执行此操作的简单代码：
Module Module1
Sub Main()
Dim input() = {"---9+6", "5+6*9+8", "6---9", "15+7*9-(7*9)", "8*9+8*9/3+5", "15*8+5", "15+(8*5)"}
For Each m As String In input
Console.WriteLine("{0} -> {1}", m, calculate(m))
Next
Dim st = Console.ReadLine()
Console.WriteLine(calculate(st))
Console.ReadKey(True)
End Sub
Dim numbers As New List(Of Double)
Public Function calculate(ByVal expression As String) As String
Try
numbers.Clear()
If String.IsNullOrWhiteSpace(expression) Then
Return ""
End If
Dim index = 0
Exp(expression, index)
If numbers.Count > 0 Then
Return numbers(0).ToString()
End If
Catch ex As Exception
Console.WriteLine(ex.Message)
End Try
Return ""
End Function
Private Sub Exp(ByVal expression As String, ByRef index As Integer)
'; E -> FE’
factor(expression, index)
primeops(expression, index)
End Sub
Private Sub primeops(ByVal expression As String, ByRef index As Integer)
'; E’ -> + F E’ | - F E’ | e
Select Case getChr(expression, index)
Case "+"
index += 1
' E() ' -> + F E’
factor(expression, index)
If numbers.Count >= 2 Then
Dim at = numbers.Count - 1
numbers(at - 1) = numbers(at - 1) + numbers(at)
numbers.RemoveAt(at)
End If
primeops(expression, index)
Case "-"
index += 1
' E() ' -> - F E’
factor(expression, index)
If numbers.Count >= 2 Then
Dim at = numbers.Count - 1
numbers(at - 1) = numbers(at - 1) - numbers(at)
numbers.RemoveAt(at)
End If
primeops(expression, index)
Case ")"
index += 1
Case Else
'; E’ -> e
End Select
End Sub
Private Sub factor(ByVal expression As String, ByRef index As Integer)
'; F -> TF’
t(expression, index)
fprime(expression, index)
End Sub
Private Sub fprime(ByVal expression As String, ByRef index As Integer)
'; F -> * T F’ | / T F’ | e
Select Case getChr(expression, index)
Case "*"
index += 1
'; F -> * T F’
t(expression, index)
If numbers.Count >= 2 Then
Dim at = numbers.Count - 1
numbers(at - 1) = numbers(at - 1) * numbers(at)
numbers.RemoveAt(at)
End If
fprime(expression, index)
Case "/"
index += 1
'; F -> / T F’
t(expression, index)
If numbers.Count >= 2 Then
Dim at = numbers.Count - 1
numbers(at - 1) = numbers(at - 1) / numbers(at)
numbers.RemoveAt(at)
End If
fprime(expression, index)
Case ")"
index += 1
End Select
'; F -> e
End Sub
Private Sub t(ByVal expression As String, ByRef index As Integer)
'T -> G | (E)
number(expression, index)
brackets(expression, index)
End Sub
Private Sub brackets(ByVal expression As String, ByRef index As Integer)
skipspace(expression, index)
If getChr(expression, index) = "(" Then
index += 1
Exp(expression, index)
End If
skipspace(expression, index)
End Sub
Private Sub number(ByVal expression As String, ByRef index As Integer)
'numbers +-[0-9]+.[0-9]+
skipspace(expression, index)
Dim sign As Integer = 1
While True
If getChr(expression, index) = "+" Then
index += 1
ElseIf getChr(expression, index) = "-" Then
index += 1
sign = -sign
Else
Exit While
End If
End While
Dim m = index
While Char.IsDigit(getChr(expression, index))
index += 1
End While
If index > m Then
If getChr(expression, index) = "." Then
index += 1
While Char.IsDigit(getChr(expression, index))
index += 1
End While
End If
Dim str = expression.Substring(m, index - m)
numbers.Add(sign * Double.Parse(str))
End If
End Sub
Private Sub skipspace(ByVal expression As String, ByRef index As Integer)
While Char.IsWhiteSpace(getChr(expression, index))
index += 1
End While
End Sub
Private Function getChr(ByVal Expressions As String, index As Integer) As Char
If index > Expressions.Length - 1 Then
Return "" '
End If
Return Expressions(index)
End Function
End Module
输出：
---9+6 -> -3
5+6*9+8 -> 67
6---9 -> -3
15+7*9-(7*9) -> 15
8*9+8*9/3+5 -> 101
15*8+5 -> 125
15+(8*5) -> 55