Block Scope

//-std=c99 -Wall -Wextra -Wpedantic -Wshadow

#include <stdio.h>
#include <stdlib.h>

int main()
{

    int a = 1;

    printf("(1a): %d\n", a);

    {
        // warning: declaration of ‘a’ shadows a previous local
        int a = 2;  //shadowed declaration is here

        int b = 2;  // OK

        printf("(2a): %d\n", a);
        printf("(2b): %d\n", b);
    }

    printf("(3a): %d\n", a);

    {
        a = 3;

        int b = 4;

        printf("(4a): %d\n", a);
        printf("(4b): %d\n", b);
    }

    printf("(5a): %d\n", a);

    return 0;
}

/*
output:

(1a): 1
(2a): 2
(2b): 2
(3a): 1
(4a): 3
(4b): 4
(5a): 3

*/