Member Avatar for abebosco 
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define TRUE 1
#define FALSE 0
#define BUFFER_LEN 240
#define NUM_P 50

void str_sort (char *[], int); 

int main ()
{
  char *s[NUM_P]; 
  int count; 
  printf("Enter the number of count:");
  scanf("%d",&count); 
  int i = 0; 

  printf("enter the first string:"); 
  scanf("%s",&s[0]);
  printf("enter the second string:"); 
  scanf("%s",&s[1]);
  printf("enter the third string:"); 
  scanf("%s",&s[2]);
  printf("enter the fourth string:"); 
  scanf("%s",&s[3]);
  printf("enter the fifth string:"); 
  scanf("%s",&s[4]);

  str_sort (s, count);
  
  printf("\n the sorted output is: \n \n");
  for (i =0; i <count; i ++)
  {
   printf("%s \n", s[i]);
   free(s[i]);
   s[i] = NULL; 
  }
}

void str_sort (char *p[], int n)
{
 char *pTemp = NULL; 
 int i = 0; 
 int sorted = FALSE; 
 while (!sorted)
 {
  sorted = TRUE; 
  for (i = 0; i <n-1; i++)
   if (strcmp(p[i], p[i+1]) > 0)
   {
    sorted = FALSE; 
    pTemp = p[i]; 
    p[i] = p[i+1];
    p[i+1] = pTemp; 
   }
 }
}

the program stops executing exactly after the 5th scanf statement .. please do help .. thanks :)

Edited by WaltP because: Added CODE tags -- with all the help about them, how could you miss using them????
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  • Latest Post Latest Post by abebosco

Dani AI

Generated

The program crashes because the string storage was never allocated and the code was passing pointer-slot addresses to a %s input, which writes bytes into whatever memory was supplied. That corrupts stack/heap metadata and yields undefined behavior — typically a crash after a few reads. correctly flagged the bad scanf usage, and confirmed that switching strategies fixed the problem.

Two safe approaches:

  • Use a fixed 2D char array (e.g., char pool[NUM_P][BUFFER_LEN]) and read into pool[i]. Do not call free() for those buffers.
  • Use an array of char *, but allocate each string with malloc() before reading and free() them afterwards. Always check malloc and input return values, and use bounded reads (field width or fgets) to avoid overflow.

Example (allocate-per-string + safe read + trim newline):

char *s[NUM_P];
for (i = 0; i < count; ++i) {
    s[i] = malloc(BUFFER_LEN);
    if (!s[i]) { perror("malloc"); exit(1); }
    if (fgets(s[i], BUFFER_LEN, stdin) == NULL) s[i][0] = '\0';
    size_t L = strlen(s[i]);
    if (L && s[i][L-1] == '\n') s[i][L-1] = '\0';
}

To sort an array of char * use qsort with a comparator rather than hand-rolled bubble sort for clarity and speed:

int cmpstr(const void *a, const void *b) {
    const char *const *pa = a;
    const char *const *pb = b;
    return strcmp(*pa, *pb);
}
/* call: qsort(s, count, sizeof s[0], cmpstr); */

Debug checklist: compile with -Wall -Wextra, run under Valgrind or ASAN to catch memory errors, check return values from scanf/fgets/malloc, and never free() memory that wasn't malloc()ed. If reading an int then lines, consume the leftover newline (or use fgets for all input) to avoid one-line shifts.

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Member Avatar for strmstn

Consider only this:

scanf("%s", &s[0]);
printf("%s", s[0]);

What happens?

Member Avatar for strmstn

Also, you are free()-ing something you haven't allocated. If you know how many strings you need, I recommend using an array of strings. Here's a working sample for you.

#include <stdio.h>
#define BUFFER_LEN 240
#define NUM_P 50
void printsample(char *[][]);
int main()
{
    char s[NUM_P][BUFFER_LEN];
    fgets(&s[0], BUFFER_LEN, stdin);
    printsample(&s);

    return 0;
}

void printsample(char *p[NUM_P][BUFFER_LEN])
{
  printf("%s", p[0]);
}
Member Avatar for abebosco

Thanks a bunch strmstn .. ur sample example really helped and finally got my program to work .. thanks again for ur quick reply :) i really appreciate it ..

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