C programming, printing 2D array using for loop, cs50

Question

I have more of a question than a problem. I am doing the CS50 introduction to computer science course and came across something that I don't understand and wondered if I could get an opinion.

I am printing a 2D array, here was my code and the first outcome.

#include <cs50.h>
#include <stdio.h>
#include <string.h>

int main (void)
{
    int a[2][3], i, j;

    //collecting values for matrix
    //rows
    for (i = 0; i < 2; i++)
    {
        //columns
        for (j = 0; j < 3; j ++)
        {
            get_int("Pls provide values for matrix: ");
        }
    }

    //printing the matrix
    for (i = 0; i < 2; i ++)
    {
        for (j = 0; j < 3; j ++)
        {
            printf("%i\t", a[i][j]);
        }
        printf("\n");
    }
}

I entered the following in my terminal as response: 1 2 3 4 5 6 this leads to this response:

 0       0       4198480                            
 0       -1885555216     32767

I changed the get_int() line to the following to get what I initially expected:

a[i][j] = get_int("Pls provide values for matrix: ");

intended actual result after change:

1       2       3
4       5       6

My question is what is the meaning/Where did the originally printed values come from? Is this something to do with the memory? My guess is that in the first run I printed values from an array that does not exist? Thank you any answer or even advice for further reading would be greatly appreciated.