THANKS

#include <cstdio>
#include <cstdlib>

struct List{
    List *next, *prev;
    int val;
};

List *head, *tail;
int stack_size;

List* new_node(int val){
    List* tmp = (List*)malloc(sizeof(List));
    tmp->next = NULL;
    tmp->prev = NULL;
    tmp->val = val;
    return tmp;
}

bool stack_empty(){
    return stack_size == 0;
}

void stack_push(int val){
    ++stack_size;
    if(stack_size == 1){
        head = new_node(val);
        tail = head;
        return;
    }
    tail->next = new_node(val);
    tail->next->prev = tail;
    tail = tail->next;
}

void stack_pop(){
    --stack_size;
    if(stack_size == 0){
        free(tail);
        head = tail = NULL;
        return;
    }
    tail = tail->prev;
    free(tail->next);
    tail->next = NULL;
}

int stack_top(){
    return tail->val;
}

void dec2bin(int num){
    for(int i = 0; i < 8; ++i){
        stack_push(num & 1);
        num >>= 1;
    }
    while(not stack_empty()){
        printf("%d", stack_top());
        stack_pop();
    }
}

int main(){
    head = NULL;
    tail = NULL;
    const char* str = "THANKS";
    for(int i = 0; str[i] != 0; ++i){
        dec2bin(str[i]);
        printf(" ");
    }
    printf("\n");
    return 0;
}