word count program

kuljule · 11-18-2008, 10:48 PM

I keep getting a segmentation error and i don't know why. Can you please help?

Thank you!

Here's the program:

insert

Code:

/*This program is suppose to take a sentence as input (in a string) and compute the number of words in the sentence.
*/



#include <stdio.h>
#include <string.h>

int main()

{
        int i, leng, number_words;
        char sentence[i];
        char *sent = sentence;
        char x;

//      while (scanf("%s", sent) == 1)
//              printf("%s\n", sent);

        scanf("%[^\n]", sent);
        printf("%s\n", sent);

        leng = strlen(sentence);
        printf("%d\n", leng);
        
        number_words=1;
        for(i=0; i<leng); i++)
        {
                if ((sentence[i] == ' ') || (sentence[i] == ','))
                        number_words = number_words + 1;
        }
         
        printf("the number of words is %d\n", number_words);
        return 0;
}

zacs7 · 11-18-2008, 10:56 PM

Code:

int i, leng, number_words;
        char sentence[i];

I assume this is C99. So it will be created with a random length since i is uninitialized.

Thus when you write to it, segfault because you probably go past the end -- who knows!

Oh and don't use scanf for strings. Use fgets() -- see the FAQ.

kuljule · 11-18-2008, 11:02 PM

What do you mean i is not initialized? Isn't it initialized in the for loop?
Also, I here bad talk about using fgets. Why do people go against using it? What's the difference between fgets and scanf of a string?

zacs7 · 11-18-2008, 11:07 PM

No, you use i when you declare 'something'.

http://cboard.cprogramming.com/showp...37&postcount=9

There is nothing wrong with using fgets(), people against using it probably have no idea why they're against it. The only bad thing is it reads in the newline (that's not bad), you can remove the newline -- see the FAQ.

kuljule · 11-18-2008, 11:14 PM

using gets(sent) doesn't change the segmentation error. But how do I initialize i?

zacs7 · 11-18-2008, 11:19 PM

Don't use gets() -- see the FAQ.

> But how do I initialize i?
Oh I don't know,

Code:

int i = 50;

maybe?

But that's only half the problem. Perhaps read the first few chapters of a good C programming book... or the tutorials on this site.

Is this for CSCI 261 class (Computer Science 1)? If so, some of your "buddies" have asked the same question in the last few days.

kuljule · 11-18-2008, 11:22 PM

Its C Programming. That's the class. The thing about initializing it means that it won't work if its greater than that number. I want to be able to do this with any length of a string. I think the segmentation error is coming from

leng = strlen(sentence);
printf("%d\n", leng);

what's the problem with this?

zacs7 · 11-18-2008, 11:25 PM

Nothing. If you're not going to listen, I won't bother.

I've told you where the segfault is coming from, FIX IT.

Ignoring the pointless pointer,

Consider this,

Code:

#define USELESS 5

char sentence[USELESS];

scanf("%s", sentence);

Now everytime your program runs, imagine USELESS changes, it could be 5, 4, -1020, 532982953. It doesn't matter. Which means you've only got enough room to store a string that big (minus the NUL character). And you'll probably write past the end -- hence the segfault. In other words 'i' can have any value an int can have.

Now consider:

Code:

char sentence[256];   /* magic number, perhaps define this somewhere. Or use BUFSIZ (look it up) */

/* TODO: check the return result of fgets() */
fgets(sentence, sizeof(sentence), stdin);

If you need "any size string" then that's a bit more advanced.

kuljule · 11-18-2008, 11:33 PM

I'm sorry if I am seeming like I'm not listening. I am, but I am just really confused. Can you repeat where the seg fault is coming from? The program prints out the sentence but then after printing it out, it says seg fault.

kuljule · 11-18-2008, 11:48 PM

nevermind figured it out. Thanks!

**Salem** · 11-18-2008, 11:52 PM

Say your random-length sentence was 5 chars, and then you read in 20 chars.

Where do the other 15 go - answer, over someone elses memory.

When do you get the segfault, when that someone else comes back to find the values they thought were safe have in fact been trashed by your sloppy code.

11-18-2008, 10:56 PM	#2
zacs7 Woof, woof! Join Date: Mar 2007 Location: Australia Posts: 3,139	Code: int i, leng, number_words; char sentence[i]; I assume this is C99. So it will be created with a random length since i is uninitialized. Thus when you write to it, segfault because you probably go past the end -- who knows! Oh and don't use scanf for strings. Use fgets() -- see the FAQ. __________________ "I.T. gets the chicky-babes" - M. Kelly bakefile \| vim Last edited by zacs7; 11-18-2008 at 10:59 PM.
zacs7 is offline

11-18-2008, 11:02 PM	#3
kuljule Registered User Join Date: Nov 2008 Posts: 27	What do you mean i is not initialized? Isn't it initialized in the for loop? Also, I here bad talk about using fgets. Why do people go against using it? What's the difference between fgets and scanf of a string?
kuljule is offline

11-18-2008, 11:07 PM	#4
zacs7 Woof, woof! Join Date: Mar 2007 Location: Australia Posts: 3,139	No, you use i when you declare 'something'. http://cboard.cprogramming.com/showp...37&postcount=9 There is nothing wrong with using fgets(), people against using it probably have no idea why they're against it. The only bad thing is it reads in the newline (that's not bad), you can remove the newline -- see the FAQ. __________________ "I.T. gets the chicky-babes" - M. Kelly bakefile \| vim Last edited by zacs7; 11-18-2008 at 11:10 PM.
zacs7 is offline

11-18-2008, 11:14 PM	#5
kuljule Registered User Join Date: Nov 2008 Posts: 27	using gets(sent) doesn't change the segmentation error. But how do I initialize i?
kuljule is offline

11-18-2008, 11:19 PM	#6
zacs7 Woof, woof! Join Date: Mar 2007 Location: Australia Posts: 3,139	Don't use gets() -- see the FAQ. > But how do I initialize i? Oh I don't know, Code: int i = 50; maybe? But that's only half the problem. Perhaps read the first few chapters of a good C programming book... or the tutorials on this site. Is this for CSCI 261 class (Computer Science 1)? If so, some of your "buddies" have asked the same question in the last few days. __________________ "I.T. gets the chicky-babes" - M. Kelly bakefile \| vim
zacs7 is offline

11-18-2008, 11:22 PM	#7
kuljule Registered User Join Date: Nov 2008 Posts: 27	Its C Programming. That's the class. The thing about initializing it means that it won't work if its greater than that number. I want to be able to do this with any length of a string. I think the segmentation error is coming from leng = strlen(sentence); printf("%d\n", leng); what's the problem with this?
kuljule is offline

11-18-2008, 11:25 PM	#8
zacs7 Woof, woof! Join Date: Mar 2007 Location: Australia Posts: 3,139	Nothing. If you're not going to listen, I won't bother. I've told you where the segfault is coming from, FIX IT. Ignoring the pointless pointer, Consider this, Code: #define USELESS 5 char sentence[USELESS]; scanf("%s", sentence); Now everytime your program runs, imagine USELESS changes, it could be 5, 4, -1020, 532982953. It doesn't matter. Which means you've only got enough room to store a string that big (minus the NUL character). And you'll probably write past the end -- hence the segfault. In other words 'i' can have any value an int can have. Now consider: Code: char sentence[256]; /* magic number, perhaps define this somewhere. Or use BUFSIZ (look it up) / / TODO: check the return result of fgets() / fgets(sentence, sizeof(sentence), stdin); If you need "any size string" then that's a bit more advanced. __________________ "I.T. gets the chicky-babes" - M. Kelly bakefile \| vim Last edited by zacs7; 11-18-2008 at 11:30 PM.*
zacs7 is offline

11-18-2008, 11:33 PM	#9
kuljule Registered User Join Date: Nov 2008 Posts: 27	I'm sorry if I am seeming like I'm not listening. I am, but I am just really confused. Can you repeat where the seg fault is coming from? The program prints out the sentence but then after printing it out, it says seg fault.
kuljule is offline

11-18-2008, 11:48 PM	#10
kuljule Registered User Join Date: Nov 2008 Posts: 27	nevermind figured it out. Thanks!
kuljule is offline

11-18-2008, 11:52 PM	#11
Salem and the hat of vanishing Join Date: Aug 2001 Location: The edge of the known universe Posts: 21,214	Say your random-length sentence was 5 chars, and then you read in 20 chars. Where do the other 15 go - answer, over someone elses memory. When do you get the segfault, when that someone else comes back to find the values they thought were safe have in fact been trashed by your sloppy code. __________________ If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut. Up to 8Mb PlusNet broadband from only £5.99 a month!
Salem is offline

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Avoiding Global variables	csonx_p	Windows Programming	32	05-19-2008 12:17 AM
brace-enclosed error	jdc18	C++ Programming	53	05-03-2007 05:49 PM
First Time Using Linked Lists, Having Trouble Replacing First Node	Peter5897	C Programming	7	06-16-2006 09:23 PM
load gif into program	willc0de4food	Windows Programming	14	01-11-2006 10:43 AM
Why wont my function exit correctly?	LightsOut06	C Programming	2	10-09-2005 09:23 PM