Question

In this piece of code, why in my testing the result is always 1, 2, and 3?

#include <stdio.h>

void test() {
    int a;
    a++;

    printf("%d",a);
}

int main(int argc, char *argv[]) {
    test();
    test();
    test();
}

I think the variable in test() is static, isn’t it? And Why?

Answer 1

As other answers told, your variable is not initialized.
It prints 1, 2 and 3 possibly because of your compiler compiled the code with prolog(prologue) that cleans the stack with zeros.

The local variables in C, actually point to the offset on your stack, and the stack frame will be restored after the call is returned.

I googled and selected a artical randomly that told about this, see [How function calls work?].

Here is a video talk about that [Assembly Programming Assembly Function Stack Frame Explained ] (again, selected randomly).

And Wikipedia explains the [Call stack] as well.