Thread: linked-list queue

I need to modify this program to use a linked-list implementation of a queue. All of the queue functions must be rewritten. The queue length needs to be defined as 6. Arrange a queue of 6 items, try to enter one more item (make sure that your program produces the warning message about overflow), then delete 3 items, enter 1 more item and display the queue. We just barely covered queues the other day so I really don't understand this too much at all. We never covered how to implement queues with linked-lists either, so this is all new to me. Here is the code I need to rewrite. Please help.

Code:

/* queue2.c */
/* a program to implement a queue using an array of int */

#include <stdio.h>
#define QSIZE 5

typedef struct{
     int elem[QSIZE];
     int front;
     int rear;
     int count;
}QType;
      
      /*    function prototypes   */
void initialize(QType *);
int empty(QType *);
int full(QType *);
int rem(QType *);
void insert(QType *, int);

main()
{
   QType Q;     /* queue declaration */
   int code, code1, i, n;
   int i1, i2;

   initialize(&Q);
   printf("initially: is empty?\n %d\n", empty(&Q));
   printf("is full?\n %d\n", full(&Q));

   printf("Enter 1 to continue, 0 to stop: ");
   scanf("%d", &code);
   while(code!=0)
   {  printf("Enter 2 to insert an item, 3 to remove an item: ");
      scanf("%d", &code1);
      switch(code1)
      {   case 2: printf("Enter an integer to be inserted: ");
                  scanf("%d", &i1);    
               /*   printf("case2: i1 is %d\n", i1); */
                  insert(&Q, i1);
                  break;
          case 3: i2=rem(&Q);
                  if(i2==0)
                    printf("Nothing is removed\n");
                  else
                    printf("%d is removed\n", i2);
                  break;
          default: printf("Wrong code\n");
      }
      printf("Currently in the queue:\n");
      if(Q.count==0)
         printf("Nothing\n");
      else
      {
      i=Q.front; n=0;
      do{
         printf("%d ", Q.elem[i]);
         n++;
         if(i>=QSIZE-1)
            i=0;
         else
            i++;
         }while(n<Q.count);   
     printf("\n");
     }
   printf("Enter 1 to continue, 0 to stop: ");
   scanf("%d", &code);
   }
   return 0;
}

void initialize(QType *q)
/* set head counter and tail counter to 0;   */
/* set counter of elements in the queue to 0 */
{   q->front=q->rear=0;
    q->count=0;
}

int empty(QType * q)
/* This function will determine if the queue is empty by        */
/* testing  the value of a counter of elements in the queue.    */
/* If the queue is empty, this function will print the message  */
/* "queue is empty" and return a value of 1.                    */
/* Otherwise, no message is displayed, and zero is returned.    */
{
   if (q->count == 0)
   { printf("QUEUE IS EMPTY\n");
     return 1;
   }
   else return 0;
}

int full(QType * q)
/* This function will determine if the queue is full by    */
/* testing the value of a counter of elements in the queue.*/
/* If the queue is full, prints "queue is full" and returns*/
/* a value of 1. Otherwise, does not print anything        */
/* and returns zero.                                       */
{
   if (q->count == QSIZE) 
   {  printf("QUEUE IS FULL\n");
      return 1; 
   }
   else return 0;
}

int rem(QType *q)
/* This function will return the item currently located  */
/* in the head of the queue. Then, the head counter      */
/* will be incremented.                                  */
{
   int temp;

   if (empty(q)) return 0;
   temp = q->elem[q->front];
   q->front=(q->front+1) % QSIZE;
   (q->count)--;
   return temp;
}

void insert(QType *q, int item)
/* The integer 'item' is inserted at the tail of the   */
/* queue and the tail counter is incremented.          */
{
   if (full(q)) return;
   q->elem[q->rear] = item;
/*   printf("in the insert: %d inserted\n", q->elem[q->rear]);*/
   q->rear = (q->rear + 1) % QSIZE;
   (q->count)++;
   return;
}