How do I create a multiple if statement in VB.NET?

Question

So I’m trying to make an infix to reverse Polish notation program by pushing the expression into a stack. The program iterates the expression looking for an operator and once it finds it, it pops the 2 values and performs the calculations. However if I try to add multiple if statements a conversion error pops. The line "if express(i) <> "+" works for addition however if I were to extend it by adding multiple conditions " if express(i) <> "+" or "-" or "*"" then it says "Conversion from string "-" to type Boolean is not valid. Could anyone help me with this? Thanks.

Module Module1

Sub Main()
 Dim expres As String
 Console.WriteLine("Enter infix expression")
 expres = Console.ReadLine()
 Dim S As New Stack
 Dim current(1) As Integer
 Dim temp_val As Integer
 For i = 0 To expres.Length - 1
 If expres(i) <> "+" Then
 S.Push(expres(i))
 End If
 If expres(i) = "+" Then
 current(0) = S.Pop().ToString
 current(1) = S.Pop().ToString
 temp_val = current(0) + current(1)
 Console.WriteLine(temp_val)
 S.Push(temp_val)
 End If
 If expres(i) = "-" Then
 current(0) = S.Pop().ToString
 current(1) = S.Pop().ToString
 temp_val = current(0) - current(1)
 Console.WriteLine(temp_val)
 S.Push(temp_val)
 End If
 If expres(i) = "*" Then
 current(0) = S.Pop().ToString
 current(1) = S.Pop().ToString
 temp_val = current(0) * current(1)
 Console.WriteLine(temp_val)
 S.Push(temp_val)
 End If
 If expres(i) = "/" Then
 current(0) = S.Pop().ToString
 current(1) = S.Pop().ToString
 temp_val = current(0) / current(1)
 Console.WriteLine(temp_val)
 S.Push(temp_val)
 End If
 If expres(i) = "^" Then
 current(0) = S.Pop().ToString
 current(1) = S.Pop().ToString
 temp_val = current(0) ^ current(1)
 Console.WriteLine(temp_val)
 S.Push(temp_val)
 End If
 If expres(i) = "~" Then
 current(0) = S.Pop().ToString
 current(1) = S.Pop().ToString
 temp_val = current(0) + current(1)
 Console.WriteLine(temp_val)
 S.Push(temp_val)
 End If
 Next
 Console.ReadLine()
End Sub

End Module

• Sebastian Brosch: can you explain the expected logic of if express(i) <> "+" or "-" or "*" more detailed?
• Hans Passant: Use a Select statement instead. Now it simply becomes the Case Else clause.

Answer 1

you should state the left expression each time you compare, something like

if express(i) <> "+" or express(i) <> "-" or express(i) <> "*"

• Mary: @freefaller "curly brackets" usually are referring to braces. I see no braces. Are you referring to the smart quotes (as MS office calls them)?
• freefaller: @Mary, yes, typing too quickly and not noticing my mistake... you are entirely correct... I mean curly braces