c - How could it be possible to read and write past the array

Question

Output of the program:

#include <stdio.h>

int main()
{
    int size;

    printf("Enter the size of array: ");
    scanf("%d",&size);

    int b[size],i = 0;
    printf("Enter %d integers to be printed: ",size);
    while(i++ < size)
    {
        scanf("%d",&b[i]);
        printf("%d     %d
", i, b[i]);
    }
    return 0;       
}

for size = 5 and input numbers :

0    1    2    3    4

is

1    0
2    1
3    2
4    3
5    4

where first column is for i and second for elements of array b.
It is clear that i in the loop while(i++ < size) { incremented to 1 before entering the loop. This loop should have to store/print the value at/of b[1], b[2], b[3], b[4] but not b[5] as loop will terminate at i = 5.
How this code is printing the value of b[5]?
I have tested it for different array size and it is not printing any garbage value.

Answer 1

By reading and writing past the array, your program invokes undefined behavior. It doesn't mean that it has to crash or print garbage values, it can pretend working fine. Apparently, that's what is happening in this case.