Why does not using C's static keyword on integers cause shell to abort when I access an array out of bounds?

I was trying to assign a value to a location outside of an array in a demo program in C. The array was of type int, and I was expecting it to overflow into the next variable I had declared, b. However, after running the program, my shell returned 1 and aborted. When I added the static keyword to the array and the integer, the program allowed me to print the value of the variable, b. However, I’m not sure why. What does the static keyword do in this context, and what difference does it make?

Take this piece of code:

#include <stdio.h>

int main(void)
{
    int a[4];
    int b;

    a[4] = 42;

    printf("%i\n", b);
}

When I run it, the program outputs 1\n zsh:abort ./memory and exits.

However, when I modify it to be the following:

#include <stdio.h>

int main(void)
{
    static int a[4];
    static int b;

    a[4] = 42;

    printf("%i\n", b);
}

The program now outputs 42. I have heard that the static keyword can have multiple uses in C, but what is it doing here that changes the program’s behavior? I have looked at many definitions and still don’t get it 🙁

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