ACPbE, Chpt3.2, ex3.6,Stacks and Queues

#include <stdio.h>
#include <stdlib.h>     //  malloc() and exit()

#define EMPTY   NULL
typedef struct  node NODE;
struct node {
    int          i;
    struct node *next;
};

// Stack Push()
NODE *pushs (NODE *stack, int i)
{
    NODE *new ;
    
    if ((new = (NODE *) malloc( sizeof(NODE))) == NULL)
    {
        printf ("errFATAL, malloc() in pushs!\n");
        exit (1);
    }
    new->i      = i ;
    new->next   = stack ;
    stack       = new ;
    return  stack ;
}

NODE *pops( NODE **stack)
{
    NODE *first;
    
    if (*stack == NULL) return NULL;
    first       = *stack ;
    *stack      = (*stack)->next; 
    first->next = NULL ;
    return first;
}


// Queue push
void pushq (NODE **q, NODE **rear, int i)
{
    NODE    *new ;
    if ((new = (NODE *)malloc(sizeof(NODE))) == NULL)
    {
        printf ("errFATAL, malloc in pushq()\n");
        exit (1);
    }
    new->i      = i ;
    new->next   = NULL ;
    if (*q == NULL) *q  = new ;  // no q add item
    else (*rear)->next  = new ;  // update (*rear)->next, queue
    *rear               = new ;
}

NODE *popq (NODE **q, NODE **rear)
{
    NODE *first ;
    first   = *q ;
    if (*q == NULL) return NULL ;    //empty Q, nothing to pop
    *q      = (*q)->next ;
    if (*q == NULL) *rear = NULL;
    first->next = NULL ;
    return first ;
}


// driver program for stack and queue

int main(void) 
{
    NODE *stack = NULL, *q = NULL, *rear = NULL, *top;
    NODE *pushs (NODE *stack, int i), *pops(NODE **stack),
         *popq  (NODE **q, NODE **rear);
    void  pushq (NODE **q, NODE **rear, int i);
    
    // Begin stack testing
    stack   = pushs (stack, 3) ;
    stack   = pushs (stack, 4) ;
    stack   = pushs (stack, 5) ;
    
    top     = pops  (&stack) ;
    printf ("Top node of stack is %d\n", top ? top->i : EMPTY ) ;
    top     = pops  (&stack) ;
    printf ("Top node of stack is %d\n", top ? top->i : EMPTY ) ;
    top     = pops  (&stack) ;
    printf ("Top node of stack is %d\n", top ? top->i : EMPTY ) ;   
    
    // Beginning queue driver
    pushq (&q, &rear, 3) ;
    pushq (&q, &rear, 4) ;
    pushq (&q, &rear, 5) ;
    
    top = popq (&q, &rear) ;
    printf ("Top node of queue is %d\n", top ? top->i : EMPTY) ;
    top = popq (&q, &rear) ;
    printf ("Top node of queue is %d\n", top ? top->i : EMPTY) ;
    top = popq (&q, &rear) ;
    printf ("Top node of queue is %d\n", top ? top->i : EMPTY) ;
    top = popq (&q, &rear) ;
    printf ("Top node of queue is %d\n", top ? top->i : EMPTY) ;
    printf("Hello World!\n");
    return 0;
}