doubt

Question

anirudhruia 0 Newbie Poster

15 Years Ago

#include<stdio.h>
int main()
{
        int n,i,j;
        char p[10][10];
        printf("please enter 10 words");
        for(i=0;i<10;i++)
        {
                for(j=0;j<10;j++)
                {
                        gets(p[i][j]) ;
                }
                printf("\n");
        }
        for(i=0;i<10;i++)
        {
                for(j=0;j<10;j++)
                {
                        printf("%c",p[i][j]);
                }
                printf("\n");
        }
        return 0;}

I actualy want to read 10 string from keyboard and print them but not gettin the output
wht to do guys:S
thanks in advance:|

c

Edited 15 Years Ago by kvprajapati because: Added [code] tags.

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Latest Post 15 Years Ago Latest Post by vinayakgarg

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Generated 10 Months Ago

Quick summary and what went wrong (based on the posts by , , and others): the code mixes unsafe input routines, misdeclared/used buffers, and incorrect string handling. Common bugs seen here: using gets() or scanf("%s", ...) without limits (buffer overflow), assigning arrays (e.g. temp[0] = p[i] — not allowed), walking past the last element (comparing p[i] with p[i+1] when i reaches the last index), and using goto to implement character-by-character comparison instead of higher-level string functions.

Safe, practical approach

Decide the maximum word length and allocate room for the terminating NUL. For example, if max 9 chars per word use buffers of length 10.
Read each line with fgets() (give the buffer size), then strip the trailing newline if present. That avoids overflow and preserves whitespace handling.
For lexicographic ordering use strcmp() to compare strings. Swap whole strings with a temporary buffer (you cannot assign arrays directly).

Example pattern (concept, not verbatim from earlier posts):

#define N 3
#define LEN 10
char p[N][LEN];
/* read each string with fgets and strip newline */
...
/* sort using strcmp; swap with a temp buffer (same LEN) */
...

Specific fixes for the posted code

Replace manual char-by-char comparison and goto with strcmp. It correctly handles end-of-string and differing lengths.
Fix swaps: declare char tmp[LEN]; and use strcpy/strncpy (careful with strncpy behavior) or memmove to copy buffers.
Fix loop bounds: bubble sort inner loop must stop before i+1 would be out of range (e.g., inner limit n-1-pass).
If you must use scanf, add a width: scanf("%9s", p[i]); for a 10-byte buffer.

Extra tips

Compile with warnings (-Wall -Wextra) and use AddressSanitizer (-fsanitize=address) when available to catch overflows.
gets() is removed from modern C; avoid it entirely.

All 7 Replies

gerard4143 371 Nearly a Posting Maven

15 Years Ago

Try something like this

#include<stdio.h>

int main()
{
	int i = 0;
	char p[10][10];
	printf("please enter 10 words\n");

	for(i = 0; i < 10; i++)
	{		
		fgets(&p[i][0], 10, stdin);
		printf("\n");
	}

	for(i = 0; i < 10; i++)
	{
		printf("%s", &p[i][0]);
		printf("\n");
	}

	return 0;
}

A few pointers..Please use code tags and never use gets() its a dangerous function.

Edited 15 Years Ago by gerard4143 because: n/a

gerard4143 371 Nearly a Posting Maven

15 Years Ago

#include<stdio.h>
int main()
{
        int i,j,pass;
        char p[3][10],temp[1][10];
        temp[0]='\0';
        printf("please enter 3 words\n");
        for(i=0;i<3;i++)
        {
                scanf("%s",&p[i]);

        }

        for(pass=0;pass<3;pass++)
        {
                for(i=0;i<3;i++)
                {
                        j=0;

                        repeat:if(p[i][j]<p[i+1][j])
                               continue;
                               else if(p[i][j]>p[i+1][j])
                               {
                                        temp[0]=p[i];
                                        p[i]=p[i+1];
                                        p[i+1]=temp[0];
                               }
                               else
                               {
                                        j++;
                                        goto repeat;
                               }
                }
        }
        for(i=0;i<3;i++)
        {
                printf("%s\n",p[i]);
        }
        return 0;
}

I'm pretty sure that your line 10

scanf("%s",&p[i]);

Is just as dangerous gets().

Try running this program

#include<stdio.h>

int main()
{
	char b[] = "test this";
	char a[10];
	

	fputs("enter a long word like Pseudopseudohypoparathyroidism->", stdout);
	scanf("%s", a);

	fprintf(stdout, "a->%s\n", a);
	fprintf(stdout, "b->%s\n", b);	
	return 0;
}

The output on my machine was

a->Pseudopseudohypoparathyroidism
b->parathyroidism

which indicates a buffer overflow.

Edited 15 Years Ago by gerard4143 because: n/a

Member #114542 commented: Good example of buffer overflow +5

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midhunps 0 Newbie Poster · Answer 1 · 2011-01-29T13:44:03+00:00

#include<stdio.h>
int main()
{
	int i;
        char p[10][10];
        printf("please enter 10 words");
        for(i=0;i<10;i++)
        {
		gets(p[i]) ;
		printf("\n");
	}
	for(i=0;i<10;i++)
	{
		puts(p[i]);
		printf("\n");
        }
        return 0;
}

try this one

Adak 419 Nearly a Posting Virtuoso · Answer 2 · 2011-01-29T19:57:15+00:00

So the advice that was given to NOT use gets(), and to USE code tags, was completely lost on you?

Try again. ;)

anirudhruia 0 Newbie Poster · Answer 3 · 2011-01-30T15:20:05+00:00

#include<stdio.h>
int main()
{
        int i,j,pass;
        char p[3][10],temp[1][10];
        temp[0]='\0';
        printf("please enter 3 words\n");
        for(i=0;i<3;i++)
        {
                scanf("%s",&p[i]);

        }

        for(pass=0;pass<3;pass++)
        {
                for(i=0;i<3;i++)
                {
                        j=0;

                        repeat:if(p[i][j]<p[i+1][j])
                               continue;
                               else if(p[i][j]>p[i+1][j])
                               {
                                        temp[0]=p[i];
                                        p[i]=p[i+1];
                                        p[i+1]=temp[0];
                               }
                               else
                               {
                                        j++;
                                        goto repeat;
                               }
                }
        }
        for(i=0;i<3;i++)
        {
                printf("%s\n",p[i]);
        }
        return 0;
}

i have modified the code but i'm still not gettin.gerard wht does fgets do
i have it to read three string and arrange them in dictionary order.please rectify this

vinayakgarg 6 Junior Poster in Training · Answer 4 · 2011-01-30T16:38:17+00:00

first you should remove any goto from your code. Always use conditional construct (if, while, for), as they are easy to manage and follow for you and avoids CPU overheads as well.

vinayakgarg 6 Junior Poster in Training · Answer 5 · 2011-01-30T21:57:33+00:00

The output on my machine was
a->Pseudopseudohypoparathyroidism
b->parathyroidism
which indicates a buffer overflow.

Thanks gerard i knew scanf was 'dangerous', but your example is a eye opener.

In my case the output was

a->Pseudopseudohypoparathyroidism
b->dohypoparathyroidism

BTW whats the meaning of this word?;)

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