stack.h

/* STACK implemented as a linked list */
#define TRUE 1
#define FALSE 0

// stack declaration
typedef struct stack
{
	int info;
	struct stack *next;
	// a node of the stack contains two information
}*NODEPTR;

// function prototypes
void initStack(NODEPTR *);   // initialize the stack
void push(NODEPTR *,int,int *); // to push information to the stack
void pop(NODEPTR *,int *,int *); // to pop an information out of the stack

// function definition

// to initalize the stack
void initStack(NODEPTR *pStack)
{
	*pStack = NULL;
}

// to push 'toPush' to the stack
void push(NODEPTR *pStack,int toPush,int *overflow)
{
	NODEPTR newNode; // node to push
	newNode = malloc(sizeof(struct stack));
	if(newNode == NULL)  // cannot create space
		*overflow = TRUE;
	else
	{
		*overflow = FALSE;
		newNode->info = toPush;
		if(*pStack == NULL)  // stack is empty
			newNode->next = NULL;
		else
			newNode->next = *pStack;
		*pStack = newNode;
	}
}

// to pop an information out of the stack
void pop(NODEPTR *pStack,int *popped,int *underflow)
{
	NODEPTR delNode; // node to remove
	if(*pStack == NULL) // empty stack
		*underflow = TRUE;
	else
	{
		*underflow = FALSE;
		delNode = *pStack;
		*popped = delNode->info;
		if(delNode->next == NULL) // contains only one node
			initStack(pStack); 
		else
			*pStack = delNode->next;  // make the next node as the first
		free(delNode); // clear space	
	}
}