Valhalla Legends Archive

I have seen tons of code in my few years of coding and more then not people use If instead of Case, when Case would make things a bit more organized.  What do you think?

You generally should use the If statement if there's a two-way comparison (yes or no; if or else). Use Select Case when you want to run multiple checks. I never use "ElseIf." Example:

Select Case Number
   Case 1
   Case 2
   Case 3
End Select

Don't do,

If Number = 1 Then
ElseIf Number = 2 Then
ElseIf Number = 3 Then
End If

This requires more CPU cycles as opposed to a Select Case.

Yeah, like what spht said, Case is much quicker, since it's a single jmp using a table, but it can't be used to compare numbers (<, >, etc.).  

Quote from: iago on November 26, 2003, 12:39 PM
Yeah, like what spht said, Case is much quicker, since it's a single jmp using a table, but it can't be used to compare numbers (<, >, etc.).  

This is probably not (always?) true for VB, because you can use Case on stuff like strings and soforth which would invalidate the optimizations possible with a C switch.

That's true.  I have no idea how it's implemented in VB, but at least in C++ it's a lot faster.

Quote from: Spht on November 26, 2003, 10:29 AM
I never use "ElseIf."

I use ElseIf every once in a while. I suppose Select Case could be used, but it don't like using that with nonconstant cases. Example:


If a Then
ElseIf b Then
ElseIf c Then
ElseIf d Then
Else
End If


vs


Select Case True
Case a
Case b
Case c
Case d
Case Else
End Select


I use Select Case wherever I can, but Select Case is somewhat limited compared to If/Then.

Quote from: Puzzle on November 28, 2003, 07:57 PM
I use Select Case wherever I can, but Select Case is somewhat limited compared to If/Then.

It is? How so?

Maybe I should rephrase. Its not exactly more limited, but gets really confusing if you would use it to replace a large nested If/Then.

Select Case is most excellent for implementing 'AND' and 'NAND' structures.  My favorite usage!

'  make sure all conditions have been met...
Result = False
Select Case False
Case A = 15
Case B$ = "Check"
Case C > 11.30
Case Else
   'all conditions true!
   Result = True
End Select
MsgBox "All Conditions have " & IIF(Result, " ", "NOT ") & "been met!"


Yes, it does work for those, but I find those much easier to understand when structured more english-language-like; "if this and that then bla".

Quote from: iago on November 26, 2003, 12:39 PM... but it can't be used to compare numbers (<, >, etc.).

iago, this is not true.  Grok even prooved it in his above example where if a specific case was greater than 11.30 then the code under it would be executed.  However, I believe grok did make a simple syntax error.  In order to do operations like that, you require the help of the 'Is' operator.


Select Case 100
   Case Is > 10
       'omg this case is greater than 10!
   Case Is < 0
       'omg this case is not less than 0!
End Select




Quote from: TheMinistered on November 29, 2003, 09:22 PM
iago, this is not true.  Grok even prooved it in his above example where if a specific case was greater than 11.30 then the code under it would be executed.  However, I believe grok did make a simple syntax error.  In order to do operations like that, you require the help of the 'Is' operator.

Code Select Expand


Select Case 100
   Case Is > 10
       'omg this case is greater than 10!
   Case Is < 0
       'omg this case is not less than 0!
End Select




I don't think there's any syntax error.  If you'll look at Grok's code, you'll see his Select statement is "Select Case False".  This means that in order to do a comparison, he needs to use the variable like C > 100 or whatever.  If he uses Is, then the statement becomes False > 100 and not the variable C that he wanted compared.

Gogo cuphead!

I was told by "professionals", that if statements were naturally quicker, is this true?

There's nothing natural about If statements.

In a language like C or C++ that imposes strict requirements on what you can have for a switch (analog of "select case"), a multiple-selection flow structure is generally much faster than a series of if statements.

This is because the compiler can often optimize the multiple-selection structure to use only one or two compares, despite there being multiple outcomes, something that generally isn't possible with if statements.

Consider the following:


int i;
// ...
switch(i) {

case 0: // ...
break;
case 1: // ...
break;
case 2: case 3: //  ...
break;
case 4: // ...
break;

}


The compiler can be clever and turn this into a table lookup that goes something like this in pseudocode:

handlerindex = handlerindextable;
handler = handlertable[handlerindex];
goto handler;

With this kind of optimization, there is no need to individually test for outcomes.

Note that because VB allows you to put almost anything into a select case construction, this optimization is probably not as applicable, so the speed difference between an if and a select case may not be as drastic as the speed difference between an if and a switch in C or C++.

Quote from: Fleet- on December 10, 2003, 07:32 AM
I was told by "professionals", that if statements were naturally quicker, is this true?

AFAIK no. When I first started in VB I did If statements for everything and was told that Case is better. Where exactly did these "professionals" work? Also, I may be wrong (and probably am) so I too would like to know. :P

Quote from: hismajesty on December 10, 2003, 02:43 PM

Quote from: Fleet- on December 10, 2003, 07:32 AM
I was told by "professionals", that if statements were naturally quicker, is this true?

AFAIK no. When I first started in VB I did If statements for everything and was told that Case is better. Where exactly did these "professionals" work? Also, I may be wrong (and probably am) so I too would like to know. :P

Work with the logic which I posted and you'll be fine.

Quote from: Grok on December 10, 2003, 01:23 PM
There's nothing natural about If statements.

They sound like natural language!

I thought polymorphism was invented to rid the world of the cases!  ;D

Quote from: Spht on December 10, 2003, 02:56 PM

Quote from: hismajesty on December 10, 2003, 02:43 PM

Quote from: Fleet- on December 10, 2003, 07:32 AM
I was told by "professionals", that if statements were naturally quicker, is this true?

AFAIK no. When I first started in VB I did If statements for everything and was told that Case is better. Where exactly did these "professionals" work? Also, I may be wrong (and probably am) so I too would like to know. :P

Work with the logic which I posted and you'll be fine.

Aye, so I was correct?