If statement

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  14 years ago

  by Miika

  Miika Suonio

  , Finland

  Joined 14 years ago

  Im using a pice of code that should read a cost from a table I ahve created. The cose is

  Private Sub Cost_Click()
  If Period = "Morning" Then
  Cost = table!Cost[Morning]
  ElseIf Period = "Afternoon" Then
  Cost = table!Cost[Afternoon]
  ElseIf Period = "Evening" Then
  Cost = table!Cost[Evening]
  ElseIf Period = "Evening" And Extension = "Yes" Then
  Cost = table!Cost[Evening Extension] else
  Cost = table!Cost[Special]
  End If
  
  
  
  
  
  
  
  
  
  

  End Sub

  What is wrong with it, it is expecting for an end of statement after each line where I have used Cost=

   

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  14 years ago

  by Miika

  Miika Suonio

  , Finland

  Joined 14 years ago

  Sorry I got it I forgot the full stops.

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  14 years ago

  by Trilarian

  Trilarian

  New Orleans, United States

  Joined 15 years ago

  Suggestion: If you have many IF-THEN statements, try using a SELECT CASE statement(I know this example doesn't have too many).  It makes the code much easier to read and modify.  For example, your above code would look like:
  
  
  Select Case Period
      Case "Morning"
          Cost = table!Cost[Morning]
      Case "Afternoon"
          Cost = table!Cost[Afternoon]
      Case "Evening"
          If Extension <> "Yes" Then
              Cost = table!Cost[Evening]
          Else
              Cost = table!Cost[Evening Extension] else
              Cost = table!Cost[Special]
          End If
  End Select
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  

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  14 years ago

  by ErwinB

  Erwin Bergsma

  Leuven, Belgium

  Joined 15 years ago

  Apart from readability, I believe that I once read somewhere that the case-statment is also quicker than the If-ElseIf-.. structure.  Can anyone confirm if this indeed is the case ?

  Erwin

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  14 years ago

  by Trilarian

  Trilarian

  New Orleans, United States

  Joined 15 years ago

  The way I was originally taught code(and that was a long time ago) was that with very small amounts of conditions, the IF statement is faster because the compiler does not have to create a hash table(table of if-then statements - select/case is converted to if/then at compile time).  However, this difference is minimal.  In some cases with larger amounts of conditions, the CASE statement pulls ahead by making use of the jump table(doesn't need to test all conditions). 
  
  That being said, I've never personally witnessed much performance gain in either direction.  I do think CASE statements are easier to look at and modify if there are more than 3 conditions or so.
  
  I did find this statement from a M$ representative from this website.
  
  Host: PaulHarrington (Microsoft)
  Q: I would like to know, if there is any performance gain on using different conditional structures ...like select-case or if-then-else-if...?
  A: In most cases there is no significant advantage. The only advantage would be for some "select-case" statements. The VB compiler can spot certain uses of select-case where it can use a "jump table" instead of a cascade of if-then-else statements.
  
  
  
  
  
  
  
  
  
  
  
  

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  14 years ago

  by ErwinB

  Erwin Bergsma

  Leuven, Belgium

  Joined 15 years ago

  Thanks for clarifying that.  I don't know why, but I tend to go for the if-elseif structure instead of the case structure, (Hey, I'm not a pro-developer...) and its good to know that it doesn't really make a difference. 

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