Trying to take multiple string inputs

Question

Practice.c

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#define ARR 32

int main(void){

  int MEM=64;
  char arr[ARR],*p=(char *)calloc(MEM,(sizeof(char))),*q=NULL;
  int i=0,j=1;

  printf("\nEnter String : ");

  while(j){

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

    if(j==1)
      strcpy(p,arr);
    else
      strcat(p,arr);


    if((j*ARR)==MEM){
      MEM=MEM+(j*ARR);
      q=realloc(p, MEM);
      if(!(q)){
        printf("\nNOT ENOUGH MEMORY\n");
        goto END;
      }
      p=q;
    }


    for(i=0;i<(strlen(arr));++i){
      if(arr[i]=='\n')
        break;
    }


    if(arr[i]=='\n')
      break;


    ++j;
  }

  printf("\n %s\n",p);


  END: free(p);p=NULL;q=NULL;

  return 0;
}

I am trying to get multiple string inputs.

I am using scanf(" %[^\n]s",arr); to take the input instead of fgets(arr,ARR,stdin);, because with fgets the program execution stops as soon as I hit ENTER key. But with scanf(" %[^\n]s",arr); the program is unable to get out of the while() loop even after entering \n.

I would like to know the mistake or mistakes I have made while writing the code.

Answer 1

The canonical way of reading multiple lines of input in C is to use fgets in a loop, like

while (fgets(arr, sizeof(arr), stdin) != NULL)
{
    if (arr_contains_special_input_to_exit_loop(arr))
        break;

    // Optionally check for and remove trailing newline from input

    // Append `arr` to your data
}

The condition to exit the loop might be some special input or an empty line or something else completely.

Answer 2

One mistake is:

for(i=0;i<(strlen(arr));++i){
  if(arr[i]=='\n')
    break;
}

Looking earlier in you code you have:

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

The [^\n] prevents any newlines \n from being contained in arr. So your loop that looks for (arr[i]=='\n') will never find any. Your next bit of code continues looking for non-existent newlines:

if(arr[i]=='\n')
  break;

This last break also breaks out of your outer loop preventing you from asking for further input on finding a newline (which it shouldn't). Fix these issues and it should get much further allowing you to enter multiple items.

---

Edit:

With a bit of effort looking at what you were doing, I now have it taking multiple input and reallocating as necessary. The strings are all concatenated and printed at the end. It could still stand a bit of work, but this should give you a few hints:

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#define ARR 32

int main (void) {

    int MEM = 64;
    char arr[ARR], *p = (char *) calloc (MEM, (sizeof (char))), *q = NULL;
    int i = 0, j = 1;


    while (j) {

        printf ("\nEnter String : ");
        scanf (" %[^\n]s ", arr);
        printf (" you entered (arr): %s\n", arr);
        if (strcmp (arr, "q") == 0) {
            printf ("\n  'q' entered, exiting.\n\n"); // provide for exit if `q` entered
            break;
        }

        if (j == 1)
            strcpy (p, arr);
        else
            strcat (p, arr);

        if ((j * ARR) == MEM) {
            MEM = MEM + (j * ARR);
            q = realloc (p, MEM);
            if (!q) {
                printf ("\nNOT ENOUGH MEMORY\n");
                goto END;
            }
            else
                printf ("\nMemory Reallocation - succeeded.\n");
            p = q;
        }
        ++j;
    }

    printf (" %s\n", p);

END:
    if (p) free (p);  /* always test pointer before calling free */
    p = NULL;
    q = NULL;

    return 0;
}

output:

./bin/me

Enter String : fishinsea
  you entered (arr): fishinsea

Enter String : alligators
  you entered (arr): alligators

Memory Reallocation - succeeded.


Enter String : really_big_mosters
  you entered (arr): really_big_mosters

Enter String : SuperSnake_Prudhome
  you entered (arr): SuperSnake_Prudhome

Memory Reallocation - succeeded.

Enter String : 8_puppies
  you entered (arr): 8_puppies

Enter String : q
  you entered (arr): q

  'q' entered, exiting.

fishinseaalligatorsreally_big_mostersSuperSnake_Prudhome8_puppies