Question on switch

[Ian Tuomi]

Is it possible to go through multiple cases in one case like this? how?

switch(foo)
{
case 1 or 2:
dosomething(); break; //dosomething if foo is either 1 or 2

case 3:
dosomethingelse(); break; // dosomethingelse if foo is 3
}

--
Ian Tuomi
Jyväskylä, Finland

"Very funny scotty, now beam down my clothes."

GCS d- s+: a--- C++>$ L+>+++$ E- W+ N+ !o>+ w---
!O- !M- t+ !5 !X R+ tv- b++ DI+ !D G e->+++ h!

NOTE: Remove NOSPAM from address

 

[Ed Morton]

Is it possible to go through multiple cases in one case like this? how?

switch(foo)
{
case 1 or 2:
dosomething(); break; //dosomething if foo is either 1 or 2

case 3:
dosomethingelse(); break; // dosomethingelse if foo is 3
}

Yes:

switch(foo)
{
case 1: /* fall through */
case 2:
dosomething();
break;
case 3:
dosomethingelse();
break;
default:
/* handle it */
break;
}

Ed.

 

[Christopher Benson-Manica]

Is it possible to go through multiple cases in one case like this? how?
Yep...

switch(foo)
{
case 1 or 2:
dosomething(); break; //dosomething if foo is either 1 or 2

case 3:
dosomethingelse(); break; // dosomethingelse if foo is 3
}

switch(foo) {
case 1: case 2:
/* do something */
break;
case 3: default:
/* do something else */
break;
}

 

[Andreas Kahari]

Is it possible to go through multiple cases in one case like this? how?

switch(foo)
{
case 1 or 2:
dosomething(); break; //dosomething if foo is either 1 or 2

case 3:
dosomethingelse(); break; // dosomethingelse if foo is 3
}

Yes:

switch (foo) {
case 1: /* FALLTROUGH /*
case 2:
bar();
break;
case 3: /* FALLTROUGH /*
case 4: /* FALLTROUGH /*
case 5:
baz();
break;
default:
quux_error();
exit(EXIT_FAILURE);
break; /* NOTREACHED */
}

 

[Ian Tuomi]

Yes:

switch (foo) {
case 1: /* FALLTROUGH /*
case 2:
bar();
break;

I'm alittle confused now.
Looking at that piece of code it looks like in case 1 nothing is done
and to access bar() it would require that foo = 2

What am I missing?

--
Ian Tuomi
Jyväskylä, Finland

"Very funny scotty, now beam down my clothes."

GCS d- s+: a--- C++>$ L+>+++$ E- W+ N+ !o>+ w---
!O- !M- t+ !5 !X R+ tv- b++ DI+ !D G e->+++ h!

NOTE: Remove NOSPAM from address

 

[A. Sinan Unur]

I'm alittle confused now.
Looking at that piece of code it looks like in case 1 nothing is done
and to access bar() it would require that foo = 2

What am I missing?

You are missing a C book that explains how the swicth statment works, and
what a break statement does. Notice that there is no break after case 1:.
Hence, when foo is equal to 1, bar will be called.

Sinan.

 

[Ian Tuomi]

You are missing a C book that explains how the swicth statment works, and
what a break statement does. Notice that there is no break after case 1:.
Hence, when foo is equal to 1, bar will be called.

Sinan.

Oh, thanks! BTW I have the K&R C book but my friend is borrowing it.

--
Ian Tuomi
Jyväskylä, Finland

"Very funny scotty, now beam down my clothes."

GCS d- s+: a--- C++>$ L+>+++$ E- W+ N+ !o>+ w---
!O- !M- t+ !5 !X R+ tv- b++ DI+ !D G e->+++ h!

NOTE: Remove NOSPAM from address

 

[Andreas Kahari]

Oops, ended the comment with /* instead of with */

I'm alittle confused now.
Looking at that piece of code it looks like in case 1 nothing is done
and to access bar() it would require that foo = 2

The case doesn't close until it's broken.

 

[Mike Wahler]

Is it possible to go through multiple cases in one case like this? how?

switch(foo)
{
case 1 or 2:

case 1:
case 2:

dosomething(); break; //dosomething if foo is either 1 or 2

case 3:
dosomethingelse(); break; // dosomethingelse if foo is 3
}

Remember that if there's no 'break' on a 'case
clause', execution falls through to the next.
So just 'stack' case values which should do
the same thing, as above.

-Mike

 

[Mike Wahler]

I'm alittle confused now.
Looking at that piece of code it looks like in case 1 nothing is done
and to access bar() it would require that foo = 2

What am I missing?

case 1:

// nothing to do here, continue to next statement

case 2:

Only a 'break' statement after case '1' and before
case '2' will cause case '2' to be skipped.

-Mike

 

[Mike Wahler]

Oops, ended the comment with /* instead of with */




The case doesn't close until it's broken.

Just like detective work.

-Mike

 

[Mark A. Odell]

You are missing a C book that explains how the swicth statment works,
and

[snip]

Oh, thanks! BTW I have the K&R C book but my friend is borrowing it.

Get it back, fast.

 

[Default User]

Oh, thanks! BTW I have the K&R C book but my friend is borrowing it.

Oh, so you HAD K&R. You'll never see it again




Brian Rodenborn

 

[Steve Zimmerman]

Is it possible to go through multiple cases in one case like this? how?

switch(foo)
{
case 1 or 2:
dosomething(); break; //dosomething if foo is either 1 or 2

case 3:
dosomethingelse(); break; // dosomethingelse if foo is 3
}

Thank you for your post, Ian.

Yes, it is possible through a technique called "fall through."

switch(foo)
{
case 1:
case 2: dosomething();
break;
...
}

The compiler will automatically execute dosomething() and break for
cases 1 and 2 You can include however many cases you want with this
technique, for example,

switch(foo)
{
case 1: /* cases 1 through 4 "fall through" to case 5 */
case 2:
case 3:
case 4:
case 5: dosomething();
break;
...
}

Cases may also be written horizontally instead of vertically, as
follows.

switch(foo)
{
case 1: case 2: case 3: case 4:
case 5: dosomething();
break;
...
}

--Steve

 

[Dik T. Winter]

>
> I'm alittle confused now.
> Looking at that piece of code it looks like in case 1 nothing is done
> and to access bar() it would require that foo = 2
>
> What am I missing?

You are missing that C differs from (for instance) Pascal. In C
statements are executed after a case until a break is encountered
or the end of the complete switch statement is reached.

 

[Irrwahn Grausewitz]

You are missing that C differs from (for instance) Pascal. In C
statements are executed after a case until a break is encountered
or the end of the complete switch statement is reached.

Right, and for a good (or was it bad?!?) example lookup
question 20.35: What is "Duff's Device"? in the c.l.c-faq:

http://www.eskimo.com/~scs/C-faq/top.html

Regards

Irrwahn

 

[Jack Klein]

Oops, ended the comment with /* instead of with */




The case doesn't close until it's broken.

There are at least two exceptions:

switch(some_val)
{
case 1:
some_func();
case 2:
some_other_func();
/* goto some_label_outside_switch */ <- uncomment this line */
yet_another_function();
} <- both cases close here, no break

some_label_outside_switch:
++some_val;

--
Jack Klein
Home: http://JK-Technology.Com
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