Variable declaration inside a switch statement.

[Srinu]

Hi all,

If we compile the below piece of code, it gets compiled. But gives
weird result.

switch(x)
{
int y=2;

case 1:
printf("%d", y);
}
What, if any, the C standard says about it?

Srinu.

[abhy]

On Oct 21, 4:00 pm, Srinu <[e-mail]:

Hi all,

If we compile the below piece of code, it gets compiled. But gives
weird result.

switch(x)
{
int y=2;

case 1:
printf("%d", y);

}

What, if any, the C standard says about it?

Srinu.

Can u tell me what weird results it gives ?

[Keith Thompson]

abhy <ab************@gmail.comwrites:

On Oct 21, 4:00 pm, Srinu <[e-mail]:

>If we compile the below piece of code, it gets compiled. But gives
weird result.

switch(x)
{
int y=2;

case 1:
printf("%d", y);

}

What, if any, the C standard says about it?

Can u tell me what weird results it gives ?

Please don't use silly abbreviations like "u" for "you". This isn't a
chat room. Take the time to spell out simple words.

Yes, showing the actual questionable output is almost always a good
idea. In this particular case, though, it's unnecessary. The
variable y is uninitialized when it's printed; any output is possible.
(Actually, the behavior is undefined, so in principle *anything* is
possible, but it will most likely print some arbitrary value of type
int.)

--
Keith Thompson (The_Other_Keith) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <* <http://users.sdsc.edu/~kst>
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"

[karthikbalaguru]

On Oct 21, 4:00 pm, Srinu <[e-mail]:

Hi all,

If we compile the below piece of code, it gets compiled. But gives
weird result.

switch(x)
{
int y=2;

case 1:
printf("%d", y);

}

What, if any, the C standard says about it?

This is a famous question in interviews :):)

A switch statement never enters at the top.
So, your initialization never gets executed.

Karthik Balaguru

[CBFalconer]

Srinu wrote:

>
If we compile the below piece of code, it gets compiled. But
gives weird result.

switch(x) {
int y=2;

case 1: printf("%d", y);
}

What, if any, the C standard says about it?

What you fail to realize is that initialization of an automatic
variable requires the generation of code. That code has to go
where the "int y = 2;" statement appears. There is no reason for
the switch statement to transfer control to that code, so y is
uninitialized (or worse) when the printf is executed.

--
Chuck F (cbfalconer at maineline dot net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home.att.net>

--
Posted via a free Usenet account from http://www.teranews.com

[CBFalconer]

abhy wrote:

Srinu <[e-mail]:

.... snip ...

>

>What, if any, the C standard says about it?

Can u tell me what weird results it gives ?

u hasn't posted in c.l.c for some time.

--
Chuck F (cbfalconer at maineline dot net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home.att.net>
--
Posted via a free Usenet account from http://www.teranews.com

[abhy]

On Oct 21, 10:43 pm, CBFalconer <[e-mail]:

abhy wrote:

Srinu <[e-mail]:

... snip ...

What, if any, the C standard says about it?

Can u tell me what weird results it gives ?

u hasn't posted in c.l.c for some time.

--
Chuck F (cbfalconer at maineline dot net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home.att.net>

--
Posted via a free Usenet account fromhttp://www.teranews.com

Hi Karthik

I didn't get the meaning of your answer " A switch statement never
enters at the top. "..?
Please explain.

[Eric Sosman]

abhy wrote On 10/22/07 16:45,:

[...]
I didn't get the meaning of your answer " A switch statement never
enters at the top. "..?
Please explain.

He means this:

switch (x) {
/*
* Nothing here will ever be executed,
* because `switch' proceeds directly
* to the chosen case or to the end of
* the entire block if no case is chosen.
*/

case 42:
/*
* This is the first piece of code that
* the `switch' can ever execute.
*/
...
}

--
Er*********@sun.com

[Srinu]

Dear friends,

Thanks a lot for your valuable suggestions.

Srinu.