Memory Allocation - General Questions

What will be the output of the program?

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

int main(void) {
    int *p = malloc(3 * sizeof(int));
    if (!p) return 1;
    p[0] = 1; p[1] = 2; p[2] = 3;
    printf("%d\n", p[0] + p[1] + p[2]);
    free(p);
    return 0;
}

What will be the output of the program?

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

int main(void) {
    double *d = calloc(3, sizeof(double));
    if (!d) return 1;
    printf("%.1f\n", d[0] + d[1] + d[2]);
    free(d);
    return 0;
}

Where is memory from malloc allocated?

Returning the address of a local variable from a function:

Freeing the same pointer twice causes: