why does the output varies for same input - c

Question

#include <stdio.h>
void fun(int *, int size, int *, int *new_size);
int main()
{
int size, new_size; // variables declaration
printf("Enter the size : "); // prompting user to enter the size of the array
scanf("%d", &size); // reading size from the user
int arr[size], arr1[size]; // declaring array of size
printf("Enter the elements into the array: "); // prompt the user to enter the elements of array
for (int i = 0; i < size; i++)
{
scanf("%d", arr + i); // reading the elements of array from user
}
fun(arr, size, arr1, &new_size); // calling function
printf("After removing duplicates: "); // prompting user a new array after removing duplicates
for (int i = 0; i < new_size; i++)
{
printf("%d ", arr1[i]);
}
printf("\n");
printf("before removing duplicates: ");
for (int i = 0; i < size; i++)
{
printf("%d ", arr[i]);
}
printf("\n");
}
void fun(int *arr, int size, int *arr1, int *new_size) // function definition
{
int count = 1; // declaring variables
arr1[0] = arr[0];
for (int i = 0; i < size; i++)
{
int flag = 0;
for (int j = 0; j < i; j++)
{
if (arr[i] == arr1[j])
{
break;
}
flag = flag + 1;
if (arr1[flag] == 0)
{
*(arr1+flag) = arr[i];
count = count + 1;
}
}
}
*new_size = count;
}
basically what i am doing is, getting the array elements and removing duplicates elements and assigning non-duplicate elements to new array,while without modifying the old array and displaying new array with modification, old array without modification.
But the problem is when i execute this code the output varies for same input values. Why is that i couldn't figure it out.
Here is the output of the program.
Enter the size : 5
Enter the elements into the array: 5
1
2
1
2
After removing duplicates: 5 1 2
before removing duplicates: 5 1 2 1 2
Enter the size : 5
Enter the elements into the array: 5
4
3
2
1
After removing duplicates: 5 4 3 2 1
before removing duplicates: 5 4 3 2 1
Enter the size : 5
Enter the elements into the array: 5
1
2
1
2
After removing duplicates: 5 1 6
before removing duplicates: 5 1 2 1 2
see the output changes