WRITE in C

Take as input a list of numbers and reverse it.

Intended approach: store the numbers in a deque (or a cardstack). Either extract the elements from the top and add it to a new queue, which will reverse the order, or traverse the list and switch the directions of the pointers.

Notice that simply exchanging the first and last pointers is not enough!

#include
#include

typedef struct s_card {
int cardvalue;
struct s_card *next;
struct s_card *prev;
} t_card;

typedef struct s_cardstack {
struct s_card *first;
struct s_card *last;
} t_cardstack;

t_cardstack *cardstackInit() {
t_cardstack *cardstack;
cardstack = malloc(sizeof(t_cardstack));
cardstack->first = NULL;
cardstack->last = NULL;
return cardstack;
}

int isEmpty(t_cardstack *cardstack) { return !cardstack->first; }

void pushFront(t_cardstack *cardstack, int cardvalue) {
t_card *node = malloc(sizeof(t_card));
node->cardvalue = cardvalue;
node->prev = NULL;
node->next = cardstack->first;
if (isEmpty(cardstack))
cardstack->last = node;
else
cardstack->first->prev = node;
cardstack->first = node;
}

void pushBack(t_cardstack *cardstack, int cardvalue) {
t_card *node = malloc(sizeof(t_card));
node->cardvalue = cardvalue;
node->prev = cardstack->last;
node->next = NULL;
if (isEmpty(cardstack))
cardstack->first = node;
else
cardstack->last->next = node;
cardstack->last = node;
}

int popFront(t_cardstack *cardstack) {
t_card *node;
int cardvalue;
if (isEmpty(cardstack))
return -1;
node = cardstack->first;
cardstack->first = node->next;
if (!cardstack->first)
cardstack->last = NULL;
else
cardstack->first->prev = NULL;
cardvalue = node->cardvalue;
free(node);
return cardvalue;
}

int popBack(t_cardstack *cardstack) {
t_card *node;
int cardvalue;
if (isEmpty(cardstack))
return -1;
node = cardstack->last;
cardstack->last = node->prev;
if (!cardstack->last)
cardstack->first = NULL;
else
cardstack->last->next = NULL;
cardvalue = node->cardvalue;
free(node);
return cardvalue;
}

int peekFront(t_cardstack *cardstack) {
if (isEmpty(cardstack))
return -1;
return cardstack->first->cardvalue;
}

int peekBack(t_cardstack *cardstack) {
if (isEmpty(cardstack))
return -1;
return cardstack->last->cardvalue;
}

void *fronttoback(t_cardstack *cardstack) {
if (isEmpty(cardstack))
return NULL;
t_card *currpointer = cardstack->first;
while (currpointer) {
printf("%d", currpointer->cardvalue);
currpointer = currpointer->next;
}
}

int main() {

int n;
scanf("%d", &n);

t_cardstack *firststack = cardstackInit();

for (int i = 0; i < n; i++) {
int x;
scanf("%d", &x);
pushBack(firststack, x);
}

// Method 1. Declare another stack and push elements
// out of the first stack into the other.

t_cardstack *revstack = cardstackInit();

// Method 2. Reverse the pointers within firststack.

return 0;
}