Case Statements Vs. If Then Statements

[captainproton]

Does anybody know which is better to use, performance wise?

For example, a simple checkbox can be evaluated in two ways;

If Checkbox1.checked then Vtemp := 100
else VTemp := 0;

or

Case Checkbox1.checked of
True: VTemp:=100;
False: VTemp:=0;
End;

My query is related to the speed at which the two work. I read somewhere that the compiler will optimise the "case" better than the "If then..". Can anyone confirm that with actual experience?

Craig

[technomage]

HI Craig

This topic may have your answers

http://www.pascalgamedevelopment.com/viewtopic.php?t=4283&highlight=case

[captainproton]

Yep, that answers my question. In fact I did read that topic some time ago but as my memory is more like my programming (full of holes) I had forgotten about it.

Someone said on that thread "great question" which is typical for me. I always come up with the cool stuff after someone else has thought of it first. Imagine my disgust when I invented the "Wheel" only to find out it had been done before.

Thanks for pointing me in the right direction. For my purposes CASE seems to be best.

Craig

[dmantione]

Well, if you just use true/false, an if might be better. However, if you have more than two cases, case is the construction to go for.

[arthurprs]

I have bech some code

Compiled on BDS2006


var
i, n, j: Integer;
begin
i := 1;
Zprofiler.Mark(1, True);
case i of
1: i := 3;
2: i := 3;
3: i := 3;

end;
Zprofiler.Mark(1, False);
Zprofiler.Mark(2, True);
if i = 1 then
i := 3 else
if i = 2 then
i := 3 else
if i = 3 then
i := 3;
Zprofiler.Mark(2, False);
Zprofiler.Mark(3, True);
case i of
3: i := 3;
2: i := 3;
1: i := 3;
end;
Zprofiler.Mark(3, False);
Zprofiler.Mark(4, True);
if i = 3 then
i := 3 else
if i = 2 then
i := 3 else
if i = 1 then
i := 3;
Zprofiler.Mark(4, False);

j := 9;
Zprofiler.Mark(5, True);
case j of
1: j := 9;
2: j := 9;
3: j := 9;
4: j := 9;
5: j := 9;
6: j := 9;
7: j := 9;
8: j := 9;
9: j := 9;
end;
Zprofiler.Mark(5, False);
Zprofiler.Mark(6, True);
if j = 1 then
j := 9 else
if j = 2 then
j := 9 else
if j = 3 then
j := 9 else
if j = 4 then
j := 9 else
if j = 5 then
j := 9 else
if j = 6 then
j := 9 else
if j = 7 then
j := 9 else
if j = 8 then
j := 9 else
if j = 9 then
j := 9;

Zprofiler.Mark(6, False);

Zprofiler.Mark(8, False);

n := 3;
Zprofiler.Mark(9, True);
case n of
1: n := 3;
2: n := 3;
3: n := 3;
end;
Zprofiler.Mark(9, False);
Zprofiler.Mark(10, True);
if n = 1 then
n := 3 else
if n = 2 then
n := 3 else
if n = 3 then
n := 3;
Zprofiler.Mark(10, False);
Zprofiler.Mark(11, True);
case n of
3: n := 3;
2: n := 3;
1: n := 3;
end;
Zprofiler.Mark(11, False);
Zprofiler.Mark(12, True);
if n = 3 then
n := 3 else
if n = 2 then
n := 3 else
if n = 1 then
n := 3;
Zprofiler.Mark(12, False);

sorry the big code :oops:

3 bechs
http://img516.imageshack.us/img516/1706/capture16072007193322ih1.th.png (http://img516.imageshack.us/img516/1706/capture16072007193322ih1.png)

http://img516.imageshack.us/img516/3881/capture16072007193317hr0.th.png (http://img516.imageshack.us/img516/3881/capture16072007193317hr0.png)

http://img516.imageshack.us/img516/4407/capture16072007193311xf3.th.png (http://img516.imageshack.us/img516/4407/capture16072007193311xf3.png)


If is better but the dif is... small¬?¬?¬?¬?

cause is better to write and manipulate

[captainproton]

@arthurprs - Thanks, that's what I wanted to see - some real evidence of speed changes.

Whilst the "case if then" question isn't vital to me it is something that I wanted to know. I am one of those guys that will spend hours pouring over my code trying to save 1kb of memory and make the exe 2kb smaller and have it run a half a second faster.

I do a lot of if a=b and b=c and c=d kind of stuff in my Slot Machine and am constantly trying to find better ways to do it.

Craig

[arthurprs]

@arthurprs - Thanks, that's what I wanted to see - some real evidence of speed changes.

Whilst the "case if then" question isn't vital to me it is something that I wanted to know. I am one of those guys that will spend hours pouring over my code trying to save 1kb of memory and make the exe 2kb smaller and have it run a half a second faster.

I do a lot of if a=b and b=c and c=d kind of stuff in my Slot Machine and am constantly trying to find better ways to do it.

Craig

;]

No problem