The wonders of select case! - GameCreators Forum

Author

Message

Tsproggy

12

Years of Service

User Offline

Joined: 2nd Jan 2012

Location: Reno, Nevada

Posted: 28th Jan 2012 19:56 Edited at: 29th Jan 2012 01:44

Link

Hello all,

I'm here posting this to inform you about the benefits of using the select case commands when speed and efficiency are required. The reason I am doing this is I see quite a bit of people on here using if statements for nearly all of their checks in their respective games or programs.

I am fairly new to DarkBASIC Proffesional but I do have previous programming experience with multiple programming languages (C# is my favorite

). I simply just want to help you improve the ways your program/games can run!

Just like you, Computers read top to bottom. When you use an If statement your computer reads it line by line through a possibly insane amount of checks depending on how many you use.

For Example:

+ Code Snippet

Age = RND(99)

If Age >= 18
  Print "You can purchase cigarettes legally in America!"
Else
  Print "You are still a minor, enjoy it while it lasts!"
EndIf

If Age >= 21
  Print "You can legally drink in America!"
Else
  Print "You can't legally drink in America. Sucks huh?"
EndIf

If Age = 22
  Print "You're my age, creepy huh?"
Else
  Print "Oh you're " + STR$(Age) + "? Good for you ^.^"
EndIf

It will read those checks 1 by 1, which seems a waste if what you're comparing doesn't meet any of the conditions above. You just wasted some time you could spend calculating critical hits or something!

So now is where I get to introduce the wonders of the select case command! Unlike the if statement it doesn't go line by line. It checks your variable to see if it fits any it's conditions and if it matches any, it jumps to it and exits when told to. Which in turn makes it faster then the if statement.

+ Code Snippet

	Select ScanCode() <-- This is the button you're currently pressing.
		Case 17 Rem W/Up <-- if it's W it jumps to here
                        Dec Player.Y,Player.Speed <-- completes this
		EndCase <-- is done
		
		Case 31 Rem S/Down <-- if it's S it jumps here
			Inc Player.Y,Player.Speed <-- does this
		EndCase <-- is done
		
		Case 30 Rem A/Left
			Dec Player.X,Player.Speed
		EndCase
		
		Case 32 Rem D/Right
			Inc Player.X,Player.Speed
		EndCase
	EndSelect

With this it'll jump to what it needs. If you where using the above code in an if statement and pressing D(Down) it would have to check through 3 other keys before it got to you

.

I hope you all understand what I've written!

I haven't failed 1,000 times! I've just found 1,000 ways something won't work.

Back to top

Profile PM

Tsproggy

12

Years of Service

User Offline

Joined: 2nd Jan 2012

Location: Reno, Nevada

Posted: 29th Jan 2012 00:48

Link

Wow.. I've had some bad luck with posting stuff on this forum for the last 2 days.. Yesterday half my message came out when posted.. and Today apparently the tags are case sensitive.

I vote there be an edit button with my post so I can fix these things.. and a preview button so I can make sure it works before I post it.

I haven't failed 1,000 times! I've just found 1,000 ways something won't work.

Back to top

Profile PM

Millenium7

19

Years of Service

User Offline

Joined: 13th Dec 2004

Location:

Posted: 29th Jan 2012 04:27

Link

are you sure it does this? after all the program needs to know 'where' to jump to. It doesn't automatically know to jump to line ~354 as opposed to ~332 when using the case command. Surely it's still checking all previous case statements top to bottom to find which one is correct before running the enclosed code

I think the reason why so many people (myself included) use the if statement is because its more readable and flexible. And in this day and age we are no longer coding for 386's with 1mb ram.

I'd like to see the difference in speed, but I have a sneaking suspicion that even over several thousand loops the difference in speed would be <1ms

Back to top

Profile PM Email

Tsproggy

12

Years of Service

User Offline

Joined: 2nd Jan 2012

Location: Reno, Nevada

Posted: 29th Jan 2012 06:14

Link

You would be wrong there sir! I have optimized a server emulator before where the coder used if statements for every check when a user right clicked an item in game. Most items in the game had a unique effect. These where literally around 1000+ items, I took out all the if statements and replaced the ones he had written in a neat Select Case(or switch) statement and I actually had quite an increase in latency (had 40+ milliseconds lag on my own local server -.-) If cut it down at least 12 ms, and you could notice a significant speed.

Also, when I used to do math programming challenges online, we would have to solve a problem or produce a result before a certain amount of time, So I would have to run a timer and stop it after I was done. I also noticed a significant difference with this.

You should try it some time, I know a select/switch statement is faster then an if statement. Also..

How is this:

+ Code Snippet

if expression
  if expression
   if expression
    if expression
     if expresssion
       if expression

easier to read then:

+ Code Snippet

Select Expression or Variable
  Case Variance
  EndCase

  Case Variance
  EndCase

  Case Variance
  EndCase

  Case Variance
  EndCase

  Case Variance
  EndCase

  Case Variance
  EndCase

EndSelect

I haven't failed 1,000 times! I've just found 1,000 ways something won't work.

Back to top

Profile PM

MrValentine

AGK Backer

13

Years of Service

User Offline

Joined: 5th Dec 2010

Playing: FFVII

Posted: 29th Jan 2012 10:48

Link

Nice...

Back to top

Profile PM

Chris Tate

DBPro Master

16

Years of Service

User Offline

Joined: 29th Aug 2008

Location: London, England

Posted: 29th Jan 2012 16:22 Edited at: 29th Jan 2012 16:35

Link

The select branch jumps to the literal that is identical to the result of the expression. The label of the case branch must BE literal ( EG: 1, 2, "3", "Cheese" or a constant: [#CONSTANT ONE = 1] ). Select 1 = 1, result is 1, so for each case, if case is 1, select case.

An if statement does not need to jump anywhere other than the line below or after the THEN keyword. If 1 = 1 Then DoThis

In other words; ask the question: If N is 10, is N lower than 3, lower than 6 and lower than 12. How could you write this easily in a select branch?

+ Code Snippet

Select n < 10
  Case n < 3
  EndCase
  Case n < 6
  EndCase
  Case n < 12
  EndCase
EndSelect

The above code will not work.

Although it is possible to do something like this:

+ Code Snippet

n = 25

Select n < 12
  Case 1
    print "Less than 12"
  Endcase
  Case Default
    print "more or equal to 12"
  Endcase
Endselect

It is recommended to use the following select statement over a series of if statements any day, it would run much faster.

+ Code Snippet

rem Pick a random function, or a default function if 0, 4 or 5 is returned

#CONSTANT ONE 1

Select Rnd(5)
  Case ONE 
    DoAction1()
  EndCase
  Case 2 
    DoAction2()
  EndCase
  Case 3 
    DoAction3()
  EndCase
  Case Default 
    DoDefaultAction()
  EndCase
EndSelect

rem Select the name of the action and perform the action
Input "Enter command: ", action$
Select Lower$( action$ )
  Case "move"
    Move Object id, 10
  EndCase
  Case "turnleft"
    Turn Object Left id, 90
  EndCase
  Case "turnright"
    Turn Object Right id, 90
  EndCase
  Case "digfortreasure"
    DigForTreasure()
  EndCase
EndSelect

If the previous results needed to be changed by the user, the if statement should be used:

+ Code Snippet

rem Pick a random function, or a default function if the variable options are not returned

FirstOption = 4
SecondOption = 2
ThirdOption = 0

option = Rnd(5)
If option = 
    DoAction1()
Else
  If option = SecondOption
    DoAction2()
  Else
    If option = ThirdOption
      DoAction3()
    Else
      DoDefaultAction()
    EndIf
  EndIf
EndIf


rem Select the name of the action and perform the action
Input "Enter command: ", action$
action$ = Lower$( action$ )
If action$ = moveAction$
  Move Object id, 10
EndIf
If action$ = moveAction$
  Turn Object Left id, 90
EndIf

rem And so on

Another handy use for select branches is to pick an array, or pointer to a variable, or a pointer to a function

+ Code Snippet

Rem Requires Matrix1 utilities
Dim Array1$(1)
Dim Array2$(1)
Dim SelectedArray$()
Array1$(1) = "Tom"
Array2$(1) = "Harry"
n$ = ""


While n$ = ""
	Input "Select array name? "; n$	
Endwhile

Select Val( n$ )
  Case "Array1"
    Link Array SelectedArray$(), Get ArrayPtr( Array1$() )
  Endcase
  Case "Array2"
    Link Array SelectedArray$(), Get ArrayPtr( Array2$() )
  Endcase
Endselect

Print "This array contains "; SelectedArray$(1)
Wait key

Back to top

Profile PM Email Website

BatVink

Moderator

21

Years of Service

User Offline

Joined: 4th Apr 2003

Location: Gods own County, UK

Posted: 29th Jan 2012 20:04

Link

SELECT statements are useful, and become more efficient when used in a state machine scenario...

CASE cPLAYING
CASE cCOLLISION
CASE cSTART
CASE cEND

In this scenario we have definite states (rather than "less than 20"). By putting them in the order that they are most frequently used, those that are infrequently used are rarely executed. In the example above, if I am PLAYING 99% of the time, with the odd COLLISION, and only STARTing and ENDing once per game, I have prevented 75% of the code running 99% of the time. If you pad this out to include the dozens of statements required per state, it all makes sense!

Back to top

Profile PM Email

Sorry your browser is not supported!

Newcomers DBPro Corner / The wonders of select case!