Double free 2

#include <stdio.h>
#include <malloc.h>

struct s{

int num;

};


int main(){

struct s *a,*b,*c,*d,*e,*f;

a =  malloc(sizeof(struct s));
printf("a is at %p \n",a);

b =  malloc(sizeof(struct s));
printf("b is at %p \n",b);

c =  malloc(sizeof(struct s));
printf("c is at %p \n",c);


free(a);
printf("Freeing a : %p \n",a);

free(c);
printf("Freeing c : %p \n",c);

free(b);
printf("Freeing b : %p \n",b);  //Bypassing top check

free(c);
printf("Freeing c : %p again \n",c); //Double free

printf("The freed bins will be added to the corresponding bins \n");
printf("Now we are again allocating memory using malloc into three pointers d,e and f \n");
printf("As they are of the same sizes as the previously allocated chunks, pointer d,e and f will get allocated the chunks that have been just free()d and added to the fastbin earlier \n ");
d = malloc(sizeof(struct s));
printf("d is at %p \n",d);

e = malloc(sizeof(struct s));
printf("e is at %p \n",e);

f = malloc(sizeof(struct s));
printf("f is at %p \n",f);

d->num = 1111;
printf("d->num is assigned to 1111 \n");

f->num = 2222;
printf("f->num is assigned to 2222 \n");

printf("Now let's print the values of the both e->num and d->num \n");


printf("d->num is %d \n ",d->num);
printf("f->num is %d \n ",f->num);

}