k&r Ex1-24 without stack

E

El kroty

Hi folks!! i'm trying to write k&r ex1-24 without a stack.
I almost have it but there's a bug that makes me crazy and
can't find it :'( whit some files it works and with others
it doesn't. Here is the code, any clues?? Thanks.

<code>
#include <stdio.h>
#include <stdlib.h>

enum states { FREE, INQUOTE, INCOMMENT, SLASH, ASTERISK, SCAPE };

int
main(void)
{
int quotes = 0;
int parenth = 0, bracket = 0, brace = 0, comment = 0;
char c;
enum states state = FREE;

while ((c = getchar()) != EOF) {
switch (c) {
case '/':
if (state == FREE)
state = SLASH;
else if (state == ASTERISK) {
comment--;
state = FREE;
}
break;
case '*':
if (state == INCOMMENT)
state = ASTERISK;
else if (state == SLASH) {
state = INCOMMENT;
comment++;
}
break;
case '"':
case '\'':
if (state == SCAPE)
state = INQUOTE;
else if (state == FREE) {
state = INQUOTE;
quotes++;
} else if (state == INQUOTE) {
state = FREE;
quotes++;
}
break;
case '(':
if (state == FREE)
parenth++;
break;
case ')':
if (state == FREE)
parenth--;
break;
case '[':
if (state == FREE)
bracket++;
break;
case ']':
if (state == FREE)
bracket--;
break;
case '{':
if (state == FREE)
brace++;
break;
case '}':
if (state == FREE)
brace--;
break;
case '\\':
if (state == INQUOTE)
state = SCAPE;
else if (state == SCAPE)
state = INQUOTE;
break;
default:
if (state == SLASH)
state = FREE;
else if (state == ASTERISK)
state = INCOMMENT;
else if (state == SCAPE)
state = INQUOTE;
}
}

if (comment != 0)
printf("Missing \'/*\' or \'*/\' in comment.\n");
if ((quotes % 2) != 0)
printf("Missing quotes.\n");
if (parenth != 0)
printf("Missing parentheses.\n");
if (bracket != 0)
printf("Missing brackets.\n");
if (brace != 0)
printf("Missing braces.\n");

exit(EXIT_SUCCESS);
}
</code>
 
E

Eric Sosman

El said:
Hi folks!! i'm trying to write k&r ex1-24 without a stack.
I almost have it but there's a bug that makes me crazy and
can't find it :'( whit some files it works and with others
it doesn't. Here is the code, any clues?? Thanks.
Click to expand...

My ancient copy of K&R only goes as high as 1-23,
so I don't know quite what you're trying to do. One of
your problems, though, is the topic of Question 12.1 in
the comp.lang.c Frequently Asked Questions (FAQ) list

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

There may, of course, be other difficulties as well.
 
M

Merrill & Michele

Eric Sosman wrote:
My ancient copy of K&R only goes as high as 1-23,
so I don't know quite what you're trying to do. One of
your problems, though, is the topic of Question 12.1 in
the comp.lang.c Frequently Asked Questions (FAQ).
Click to expand...

K&R2 ex 1-24: Write a program to check a C program for rudimentary syntax
errors like unbalanced parentheses, brackets and braces. Don't forget about
the quotes, both single and double, escape sequences, [sic] and comments.
(This program is hard to do in full generality.)

I think it's ironic that an exercise to detect rudimentary errors contains
the first English error I've read from K&R. ( A comma can precede the
terminal 'and' in a list or not, but the style MUST remain consistent.)

As far as getting this with or without a stack, my only contribution will be
to state the exercise clearly. MPJ
 
D

Daniel Fischer

Merrill said:
As far as getting this with or without a stack, my only contribution will
be to state the exercise clearly.
Click to expand...

#include "weak joke involving 'the state of the machine'"


Daniel
 
H

Herbert Rosenau

Hi folks!! i'm trying to write k&r ex1-24 without a stack.
I almost have it but there's a bug that makes me crazy and
can't find it :'( whit some files it works and with others
it doesn't. Here is the code, any clues?? Thanks.

<code>
#include <stdio.h>
#include <stdlib.h>

enum states { FREE, INQUOTE, INCOMMENT, SLASH, ASTERISK, SCAPE };

int
main(void)
{
int quotes = 0;
int parenth = 0, bracket = 0, brace = 0, comment = 0;
char c;
Click to expand...

Bug!

getchar returns int not char.
enum states state = FREE;

while ((c = getchar()) != EOF) {
switch (c) {
case '/':
if (state == FREE)
state = SLASH;
else if (state == ASTERISK) {
comment--;
state = FREE;
}
break;
case '*':
if (state == INCOMMENT)
state = ASTERISK;
else if (state == SLASH) {
state = INCOMMENT;
comment++;
}
break;
case '"':
case '\'':
if (state == SCAPE)
state = INQUOTE;
else if (state == FREE) {
state = INQUOTE;
quotes++;
} else if (state == INQUOTE) {
state = FREE;
quotes++;
}
break;
case '(':
if (state == FREE)
parenth++;
break;
case ')':
if (state == FREE)
parenth--;
break;
case '[':
if (state == FREE)
bracket++;
break;
case ']':
if (state == FREE)
bracket--;
break;
case '{':
if (state == FREE)
brace++;
break;
case '}':
if (state == FREE)
brace--;
break;
case '\\':
if (state == INQUOTE)
state = SCAPE;
else if (state == SCAPE)
state = INQUOTE;
break;
default:
if (state == SLASH)
state = FREE;
else if (state == ASTERISK)
state = INCOMMENT;
else if (state == SCAPE)
state = INQUOTE;
}
}

if (comment != 0)
printf("Missing \'/*\' or \'*/\' in comment.\n");
if ((quotes % 2) != 0)
printf("Missing quotes.\n");
if (parenth != 0)
printf("Missing parentheses.\n");
if (bracket != 0)
printf("Missing brackets.\n");
if (brace != 0)
printf("Missing braces.\n");

exit(EXIT_SUCCESS);
}
</code>
Click to expand...
 
P

Peter Shaggy Haywood

Groovy hepcat Merrill & Michele was jivin' on Thu, 21 Oct 2004
11:36:38 -0500 in comp.lang.c.
Re: k&r Ex1-24 without stack's a cool scene! Dig it!
I made no joke, Junge; you're OT. MPJ
Click to expand...

No, no, Daniel made the joke, and one alluding to the way (or *a*
way, at least) to do the parsing required to check for syntax errors.
And humour is always on topic. :)

--

Dig the even newer still, yet more improved, sig!

http://alphalink.com.au/~phaywood/
"Ain't I'm a dog?" - Ronny Self, Ain't I'm a Dog, written by G. Sherry & W. Walker.
I know it's not "technically correct" English; but since when was rock & roll "technically correct"?
 
D

Dave Thompson

Hi folks!! i'm trying to write k&r ex1-24 without a stack.
I almost have it but there's a bug that makes me crazy and
can't find it :'( whit some files it works and with others
it doesn't. Here is the code, any clues?? Thanks.
Click to expand...

Aside from some minor points marked below and the (char)EOF issue
noted already -- which is only a problem on some platforms, and
obviously not yours or it would always hang -- I don't see any
problems. There are of course some errors you can make it doesn't
catch, but that's inherent in the stated problem/requirement. Can you
give a minimal or at least small test case on which it falsely reports
an error, or fails to report an error (you think) it should catch?
switch (c) {
case '/':
if (state == FREE)
state = SLASH;
else if (state == ASTERISK) {
comment--;
state = FREE;
}
break;
case '*':
if (state == INCOMMENT)
state = ASTERISK;
else if (state == SLASH) {
state = INCOMMENT;
comment++;
}
break;
Click to expand...

Your variable 'comment' looks like it is trying to count nesting
level, but C comments don't nest and your state machine correctly
implements that, so the variable is essentially redundant.
case '"':
case '\'':
if (state == SCAPE)
state = INQUOTE;
else if (state == FREE) {
state = INQUOTE;
quotes++;
} else if (state == INQUOTE) {
state = FREE;
quotes++;
}
break;
Click to expand...

You won't catch a mismatch of "..' or '..". That is arguably not a
"rudimentary" error, but can be handled by a straightforward extension
of what you have already.
case '(':
if (state == FREE)
parenth++;
break;
case ')':
if (state == FREE)
parenth--;
break;
case '[':
if (state == FREE)
bracket++;
break;
case ']':
if (state == FREE)
bracket--;
break;
case '{':
if (state == FREE)
brace++;
break;
case '}':
if (state == FREE)
brace--;
break;
case '\\':
if (state == INQUOTE)
state = SCAPE;
else if (state == SCAPE)
state = INQUOTE;
break;
default:
if (state == SLASH)
state = FREE;
else if (state == ASTERISK)
state = INCOMMENT;
else if (state == SCAPE)
state = INQUOTE;
}
}

if (comment != 0)
printf("Missing \'/*\' or \'*/\' in comment.\n");
Click to expand...

You don't need to escape ' in a "string", although it is legal if you
want to. The only situation 'comment != 0' can detect given the state
machine above is a final open /* with no */, so the output might more
accurately be something like "Unclosed comment". And you could drop
the variable and just check state == COMMENT or == ASTERISK.
if ((quotes % 2) != 0)
printf("Missing quotes.\n");
Click to expand...

Again state == INQUOTE or == SCAPE would be as good.
if (parenth != 0)
printf("Missing parentheses.\n");
if (bracket != 0)
printf("Missing brackets.\n");
if (brace != 0)
printf("Missing braces.\n");
Click to expand...
I would describe these as "mismatched". It could be an open for which
the close is missing, or an "extra" or "stray" open that shouldn't be
there in the first place; or vice versa.

- David.Thompson1 at worldnet.att.net
 

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