Something is wrong with my bubble sort output - c

Question

This is just a normal bubble sort code, but something is wrong in it.
#include <stdio.h>
#include <stdlib.h>
void bubble_sort(int size, int *arr);
int main(void)
{
int *array, size;
printf("enter the amount of data: ");
scanf("%d", &size);
array = (int*)malloc(sizeof(int) * size);
for (int i = 0; i < size; ++i)
{
scanf("%d", &array[i]);
}
bubble_sort(size, array);
for (int i = 0; i <= size; ++i)
{
printf("%d ", array[i]);
}
printf("\n");
return 0;
}
void bubble_sort(int size, int *arr)
{
for (int i = 0; i < size; ++i)
{
for (int j = 0; j < size; ++j)
{
if (arr[j] > arr[j + 1])
{
int temp;
temp = arr[j];
arr[j] = arr[j + 1];
arr[j + 1] = temp;
}
else if (arr[j] == arr[j + 1])
{
continue;
}
}
}
}
When I execute it, a zero appear in the output when it must be print 1 2 3
[my_username#my_computer bubble_sort]$ ./bubble_sort
enter the amount of data: 3
3 1 2
0 1 2 3
^
|
Where are this zero came from?

Answer 1

Well, it is not quite Bubble Sort.
To start, as pointed out in the comments: arr[j + 1] accesses the array with an invalid index - one past the end of the array when j is at its maximum value (size - 1).
The loop to print the array
for(int i = 0; i <= size; ++i)
has a similar off-by-one error. i < size is the desired condition.
Accessing an array out-of-bounds invokes Undefined Behaviour.
The else if block within the sort is superfluous.
The simplified variant of bubble sort is usually written as:
void bubble_sort(int *array, size_t length)
{
for (size_t i = 0; i < length; i++) {
for (size_t j = i + 1; j < length; j++) {
if (array[i] > array[j]) {
int temp = array[i];
array[i] = array[j];
array[j] = temp;
}
}
}
}
Whereas the standard bubble sort stops if it makes a pass on the array without swapping.
void bubble_sort(int *array, size_t length)
{
int swapped;
do {
swapped = 0;
for (size_t i = 1; i < length; i++) {
if (array[i - 1] > array[i]) {
int temp = array[i - 1];
array[i - 1] = array[i];
array[i] = temp;
swapped = 1;
}
}
} while (swapped);
}
This can be optimized by observing that all elements after the last swap have already been sorted.
void bubble_sort(int *array, size_t length)
{
do {
size_t n = 0;
for (size_t i = 1; i < length; i++) {
if (array[i - 1] > array[i]) {
int temp = array[i - 1];
array[i - 1] = array[i];
array[i] = temp;
n = i;
}
}
length = n;
} while (length);
}