what's the prob with goto

[Vishal Naidu]

i m new to the C world...

i ve been told by my instructors not to use goto stmt..
but no one could give me a satisfactory answer as to why it is so..

plz help me out of this dilemma, coz i use a lot of goto in my codes....

[Muni]

Even though goto were not used directly, but they are implicitly part
of control constructs of a programming lang.

gotos would reduce the redability of the program. If the programming
spanning across pages, it owuld be really difficult to understand the
programs with gotos.

[Richard Heathfield]

Vishal Naidu said:

i m new to the C world...

i ve been told by my instructors not to use goto stmt..
A wise student obeys his instructors unless he knows them to be wrong.
but no one could give me a satisfactory answer as to why it is so..
Not all instructors understand the advice they give. That doesn't
necessarily mean it is bad advice.
plz help me out of this dilemma, coz i use a lot of goto in my codes....

The problem is that goto doesn't scale well. The more you use it, the harder
your programs will be to maintain, because the flow of control of your
program becomes harder to read. This phenomenon is known as "spaghetti
code", and with good reason.

In many organisations, goto is actually banned altogether. So it's a good
idea to learn how to program without it. Once you have done so, you'll
wonder what you ever saw in it.
--
Richard Heathfield
"Usenet is a strange place" - dmr 29 July 1999
http://www.cpax.org.uk
Email rjh at the above domain

[John Bode]

Vishal Naidu wrote:

i m new to the C world...

i ve been told by my instructors not to use goto stmt..
but no one could give me a satisfactory answer as to why it is so..

plz help me out of this dilemma, coz i use a lot of goto in my codes....

Bad structured code is orders of magnitude easier to debug and maintain
than bad unstructured code.

You shouldn't need to use goto very often. One problem with using goto
is that it can destroy the ability to debug code by inspection. It's
not so much the goto itself that's the problem, but rather than the
uncertainty introduced in the code around the target of the goto. For
instance, given the code fragment:

i = 7;
label: printf("%d\n", i);

What value gets printed for any particular path of execution? Until I
account for every instance of "goto label;", I don't know. I have to
trace all possible paths of execution before I can say with any
confidence what gets printed under what conditions. This makes code
harder to debug and maintain. God forbid I have to make any changes,
because I can't say with any confidence that any change will not
inadvertantly affect *some* path of execution.

The story I like to tell is one program I stumbled across early in my
career written by an electrical engineer. A 5000-line main() function,
with something 15 gotos, some of which branched forward, some backward.
It took my co-worker two full weeks to figure out how the damn thing
actually worked. We were tasked with improving performance of the app,
but anything we did simply broke the code. We finally recommended that
the customer just buy faster hardware; it would be cheaper than the
effort to make the code faster would cost.

Now, that particular application was pathological beyond the use of
gotos, but they made a bad situation impossible. Had the code been
somewhat structured, we probably could have made some improvements.

Gotos are useful in a limited set of circumstances, like when you need
to break out of a deeply nested loop, or need to make sure some cleanup
code runs before exiting a routine. But they should not replace
control structures like if-else , for, while, do-while, or switch
statements.

If you're going to use a goto, make sure you branch forward *only*, and
that you do not branch into a block.

[Ian Malone]

Richard Heathfield wrote:

The problem is that goto doesn't scale well. The more you use it, the harder
your programs will be to maintain, because the flow of control of your
program becomes harder to read. This phenomenon is known as "spaghetti
code", and with good reason.

In many organisations, goto is actually banned altogether.

<snip>

But that's okay, because you can achieve similar functionality with
a for loop, a switch statement and liberal application of control
variables. <g>

--
imalone

[Lew Pitcher]

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Vishal Naidu wrote:

i m new to the C world...

i ve been told by my instructors not to use goto stmt..
but no one could give me a satisfactory answer as to why it is so..

plz help me out of this dilemma, coz i use a lot of goto in my codes....

Please read "Goto Statement Considered Harmfull" by Dr. Dijkstra, in the
"Communicat ions of the ACM". You can find a public version of this paper at
http://www.acm.org/classics/oct95/
- --
Lew Pitcher
IT Specialist, Enterprise Data Systems,
Enterprise Technology Solutions, TD Bank Financial Group

(Opinions expressed are my own, not my employers')
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[ajm]

Vishal,

John's point about goto into a block is real important, for example if
you skip past the initialisation of certain local variables then the
results can be "undefined" - e.g., static local variables. The C
reference manual (and doubtless other publications) make specific note
of this issue so you have been warned ;)

ajm.

[Eric Sosman]

ajm wrote:

Vishal,

John's point about goto into a block is real important, for example if
you skip past the initialisation of certain local variables then the
results can be "undefined" - e.g., static local variables. The C
reference manual (and doubtless other publications) make specific note
of this issue so you have been warned ;)

The warning is good, but the detail is not: a static
variable cannot be uninitialized, and furthermore its
initialization occurs before the program starts and thus
does not depend on the run-time flow of execution. The
problem ajm mentions afflicts auto and register variables,
but not statics.

--
Eric Sosman
es*****@acm-dot-org.invalid

[ajm]

apologies! yes of course that is what I meant to say (statics are
handled entirely differently as Eric points out)

[osmium]

"Vishal Naidu" writes:

i m new to the C world...

i ve been told by my instructors not to use goto stmt..
but no one could give me a satisfactory answer as to why it is so..

plz help me out of this dilemma, coz i use a lot of goto in my codes....

If the instructor had taught the course properly you wouldn't be using a lot
of gotos, because you wouldn't even no the stmt existed till the last day of
the course.