/** A structure type representing a node in the linked list.
* Each node contains a pointer to the next node in the list, and a
* character field
*/
typedef struct node {
// Student must fill in the node structure
} Node;

/** A structure representing a stack based around a linked list.
*/
typedef struct {
    Node *head; //!< A pointer to the head item in the linked list.
    int count; //!< How many nodes have been added to the list?
    int size; //!< How many nodes may be added to the list?
} Stack;

/** Create a new Stack and return a pointer to it.
*
* \param size How many items can the new stack hold?
*/
Stack *create_stack(int size);

/** Release the memory associated with the specified stack.
*
* \param release A pointer to the Stack to free.
*/
void free_stack(Stack *release);

/** Push a character onto the stack. This adds the specified character to the
* top of the stack. If the push fails (because memory could not be allocated
* for the new stack item), this will exit the program with an error.
*
* \param stack A pointer to the stack to push the character onto.
* \param c The character to push onto the top of the stack.
*/
void push(Stack *stack, char c);

/** Pop a character off the stack, and return the chracter. This removes the
* top item from the stack, and returns the character that was stored there.
*
* \param stack A pointer to the stack to pop an item off.
* \return The character that was at the top of the stack, or -1 if the stack
* is empty.
*/
char pop(Stack *stack);

/** Determine whether the stack is empty.
*
* \param stack A pointer to the stack to check for items.
* \return true (non-zero) if the stack is empty, false (zero) if it contains
* one or more entries.
*/
int isempty(Stack *stack);

/** Check whether the stack is full. This determines whether it is possible
* to create a new stack item, and if it is this returns false. If a new
* item can not be allocated, this returns true.
*
* \param stack A pointer to the stack to check the capacity of.
* @return true (non-zero) if the stack is full, false (zero) if it is not.
*/
int isfull(Stack *stack);