Posts: 374
Threads: 56
Joined: Apr 2022
Reputation:
13
Other than code efficiency, I'm wondering why I would nest an Else statement v's using multiple ElseIf statements. You guys nest your Elses? or go with ElseIF's
For example"
NESTED ELSE
If (condition) then
....
Else
If (condition) then
....
Else
If (condition) then
....
Else
If (condition) then
End if
End if
End if
UNNESTED ElseIF
If (condition) then
....
ElseIf (condition) then
....
ElseIf (condition) then
....
ElseIf (condition) then
...
End if
Just curious
Posts: 2,686
Threads: 326
Joined: Apr 2022
Reputation:
215
In such cases, I try to go with SELECT CASE, nested between IF statements, just for the difference in visibility of flow for me.
Too many ELSEIFs, and I get lost trying to track and keep up with them all. Instead, I'll swap to independent IFs and GOTOs, to keep my brain organized better.
IF (condition) THEN
stuff
GOTO done_iffing_around
END IF
IF (next condition...
same
IF (same for 4 more ELSEIF type things...
same
END IF
done_iffing_around:
Posts: 1,277
Threads: 120
Joined: Apr 2022
Reputation:
100
I depends on the situation I suppose. Take this rectangular collision code for example:
IF R1.right >= R2.left THEN ' check for overlapping coordinates
IF R1.left <= R2.right THEN
IF R1.bottom >= R2.top THEN
IF R1.top <= R2.bottom THEN ' all checks passed, must be a collision
RectCollide% = -1 ' return that a collision was detected (TRUE)
END IF
END IF
END IF
END IF
ELSEIF would not work in this case. Also, at any point one of the IF statements becomes FALSE the remaining IF statements are skipped, speeding up the process.
I'm with Steve on this as well. For a situation where many ELSEIFs are required I would rather use SELECT CASE because of its clean style and easy readability.
New to QB64pe? Visit the QB64 tutorial to get started.
QB64 Tutorial
Posts: 649
Threads: 95
Joined: Apr 2022
Reputation:
22
(08-17-2024, 03:35 PM)SMcNeill Wrote: In such cases, I try to go with SELECT CASE, nested between IF statements, just for the difference in visibility of flow for me.
Too many ELSEIFs, and I get lost trying to track and keep up with them all. Instead, I'll swap to independent IFs and GOTOs, to keep my brain organized better.
IF (condition) THEN
stuff
GOTO done_iffing_around
END IF
IF (next condition...
same
IF (same for 4 more ELSEIF type things...
same
END IF
done_iffing_around:
GoTo??? Wash yer mouth out!
I've gotten the impression I'm about the only one who uses this outdated command! 
Posts: 2,128
Threads: 218
Joined: Apr 2022
Reputation:
100
I tend to use SELECT CASE whenever possible so I don't if it up too much. It has that neat SELECT EVERYCASE, too. My next favorite is the ELSEIF, which is useful in some situations. I have done some routines like Terry's example with block nested If/then statements and They are easy enough to read and understand, due to the progressive indenting.
Pete
Fake News + Phony Politicians = Real Problems
Posts: 374
Threads: 56
Joined: Apr 2022
Reputation:
13
I think Terry your nested IF statements would only perform the next test IF the last one was true. Otherwise, as you point out, IF any of the conditions test False no other conditions are tested.
I'm thinking if your code did include Else in the nesting then I think all the conditions would be tested...I think...
IF R1.right >= R2.left THEN ' check for overlapping coordinates
Else
IF R1.left <= R2.right THEN
Else
IF R1.bottom >= R2.top THEN
Else
IF R1.top <= R2.bottom THEN ' all checks passed, must be a collision
RectCollide% = -1 ' return that a collision was detected (TRUE)
END IF
END IF
END IF
END IF
IF R1.right >= R2.left THEN ' check for overlapping coordinates
ElseIF R1.left <= R2.right THEN
ElseIF R1.bottom >= R2.top THEN
ElseIF R1.top <= R2.bottom THEN ' all checks passed, must be a collision
RectCollide% = -1 ' return that a collision was detected (TRUE)
END IF
Both Else and ElseIF would test each condition, without the Else or ElseIF conditions are tested until a False is incurred....I thinks that's correct. Your code would short circuit the IF run and that could save a lot of time in processing
Posts: 2,686
Threads: 326
Joined: Apr 2022
Reputation:
215
This was actually a very interesting exercise in backwards logic. @TerryRitchie @Dimster -- Both of you see if this kind of odd scenario appeals to you:
Code: (Select All)
Screen _NewImage(640, 480, 32)
$Color:32
Do
Cls
Line (100, 100)-(200, 200), Red, BF
Line (300, 100)-(400, 200), Blue, BF
While _MouseInput: Wend
x = _MouseX: y = _MouseY
If x >= 100 Then
If x <= 200 Then
If y >= 100 Then
If y <= 200 Then
_PrintString (140, 140), "OK!"
End If
End If
End If
End If
If x < 300 Then
ElseIf x > 400 Then
ElseIf y < 100 Then
ElseIf y > 200 Then
Else
_PrintString (340, 140), "OK!"
End If
_Limit 30
_Display
Loop Until _MouseButton(1)
Run that. There's two boxes on the screen and we check mouse collision with each of them.
The left box uses Terry's style collision to see if the mouse is inside the box or not. For it to trigger, the mouse must be inside each x/y bound.
The right box uses If and ElseIf to exclude the *outsides* of the box, so that the final ELSE has to be the only points left that aren't excluded by our X/Y bounds.
Both works, but the second is so foreign to my usual way of thinking that it blows my mind. We're literally "thinking outside the box" here!
Posts: 374
Threads: 56
Joined: Apr 2022
Reputation:
13
That's pretty cool Steve.
Posts: 2,128
Threads: 218
Joined: Apr 2022
Reputation:
100
08-19-2024, 09:52 PM
(This post was last modified: 08-19-2024, 09:53 PM by Pete.)
Well jus ah dadburn minute there ya galoots...
How's about SELECT CASEY?
Code: (Select All)
Screen _NewImage(640, 480, 32)
$Color:32
Do
Cls
Line (100, 100)-(200, 200), Red, BF
Line (300, 100)-(400, 200), Blue, BF
While _MouseInput: Wend
x = _MouseX: y = _MouseY
Select Case x
Case 100 To 200
Select Case y
Case 100 To 200
_PrintString (130, 140), "Pete!"
End Select
End Select
If x < 300 Then
ElseIf x > 400 Then
ElseIf y < 100 Then
ElseIf y > 200 Then
Else
_PrintString (330, 140), "Steve"
End If
_Limit 30
_Display
Loop Until _MouseButton(1)
- Sam
Fake News + Phony Politicians = Real Problems
Posts: 1,277
Threads: 120
Joined: Apr 2022
Reputation:
100
08-19-2024, 10:05 PM
(This post was last modified: 08-19-2024, 10:07 PM by TerryRitchie.)
That second method caused my brain to get stuck in an infinite loop ... or it possibly divided by 0, I can't tell which, LOL
Yeah, that's odd looking but works.
Way to butcher SELECT CASE Pete! But hey, it works too.
New to QB64pe? Visit the QB64 tutorial to get started.
QB64 Tutorial
|
