C - why is arr[0] showing as 32767 - c

Question

Following is just one section on one code.
t is test case number and then i have integer n for each t.
i want to break integer to digits and store in array and then print each element of array.
input
1
45
expected output
5
4
actual output
32767
0
code
#include <stdio.h>
#include <string.h>
#include <math.h>
#include <stdlib.h>
int main() {
int t,n,n1,tmp,in,len,j;
scanf("%d",&t);
while(t--)
{
scanf("%d",&n);
int arr[]={};
n1=n;
in=0;
len=0;
while(n1>0)
{
tmp=n1%10;
arr[in]=tmp;
len++;
n1=n1/10;
in++;
}
for(j=0;j<len;j++)
{
printf("%d\n",arr[j]);
}
}
}

Answer 1

The problem is with your definition of int arr[]={}; which creates an empty array without space for storage. You are better off always defining a maximum array size, unless dynamically allocating. Fixing that issue (along with initializing all values) takes care of the issue.
The following is just one approach to correcting the issue. It defines a maximum number of array elements MAXVALUES of 128. It also adds prompts to orient the user to the data requested, and prevents the trailing newline from your first use of scanf from being read as the input for 'n':
#include <stdio.h>
#include <stdlib.h>
#define MAXVALUES 128
int main () {
int t = 0;
int n = 0;
int n1 = 0;
int tmp = 0;
int in = 0;
int len = 0;
int j = 0;
printf ("\n Enter the number of numbers to convert: ");
scanf ("%d%*c", &t);
while (t--) {
printf ("\n Enter the number 'n' : ");
scanf ("%d%*c", &n);
int arr[MAXVALUES] = {0};
in = 0;
len = 0;
n1 = n;
while (n1 > 0) {
tmp = n1 % 10;
arr[in] = tmp;
len++;
n1 = n1 / 10;
in++;
}
for (j = 0; j < len; j++) {
printf ("%d\n", arr[j]);
}
}
return 0;
}
output:
$ ./bin/arrayval
Enter the number of numbers to convert: 2
Enter the number 'n' : 12345
5
4
3
2
1
Enter the number 'n' : 56789
9
8
7
6
5
Dynamically Allocate arr based on digits in n
You can dynamically allocate arr to prevent having #define allocate more space than needed (this is kinda like using a sledge-hammer to swat a fly here). It just takes a little more work. Specifically, it takes knowing how many digits are in n before you allocate arr so you can allocate no more memory than needed. Here, the number of digits in n is calculated by the function szitoa and then arr is allocated. This is one approach to that type solution:
#include <stdio.h>
#include <stdlib.h>
#include <limits.h>
/* determine number of chars required for string of int i,
does NOT include space for null char (like strlen) */
size_t
szitoa (int val)
{
int it = 0;
int sz = (val > 0) ? 0 : 1; /* provide space of '-' */
val = (val > 0) ? val : -val; /* absolute value */
for (it = 1; it < INT_MAX; it*=10) {
sz++;
if (val >= it && val < (it*10))
break;
}
return sz;
}
int main () {
int t = 0;
int n = 0;
int n1 = 0;
int tmp = 0;
int in = 0;
int len = 0;
int j = 0;
printf ("\n Enter the number of numbers to covert: ");
scanf ("%d%*c", &t);
while (t--) {
printf ("\n Enter the number 'n' : ");
scanf ("%d%*c", &n);
/* dynamically allocate arr and validate */
int *arr = calloc (szitoa (n), sizeof (int));
if (!arr) {
fprintf (stderr, "error: arr allocation failed\n");
exit (EXIT_FAILURE);
}
in = 0;
len = 0;
n1 = n;
while (n1 > 0) {
tmp = n1 % 10;
arr[in] = tmp;
len++;
n1 = n1 / 10;
in++;
}
for (j = 0; j < len; j++) {
printf ("%d\n", arr[j]);
}
if (arr) free (arr); /* free memory allocated to arr */
}
return 0;
}

Answer 2

This should work for you:
#include <stdio.h>
int main() {
int number, numberCount, tmp, count;
printf("Please enter a number:\n>");
scanf("%d", &number);
tmp = number;
for(numberCount = 0; tmp > 0; numberCount++)
tmp /= 10;
int numbers[numberCount];
for(count = (numberCount-1); number > 0; count--) {
numbers[count] = number % 10;
number /= 10;
}
for(count = 0; count < numberCount; count++)
printf("%d digit is: %d\n", count+1, numbers[count]);
return 0;
}
Input:
45
Output:
1 digit is: 4
2 digit is: 5

Answer 3

You are trying to write more integers to your array than you have allocated space for. This code here:
while(n1>0)
{
tmp=n1%10;
arr[in]=tmp; // You initialize the array space to in, which is ambiguous.
len++;
n1=n1/10;
in++; // You increment the array after already initializing space which you can't do in this manner.
}
If you wish to accomplish in expanding your array based on the number of inputs from the user which is also ambiguous - you might think about using dynamic memory.