Trying to take multiple string inputs - c

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