UNIT 3: QUEUE Programs demonstrated in class. Tojo Mathew Asst. Professor CSE Dept., NIE Mysuru.

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1 UNIT 3: QUEUE Programs demonstrated in class. Tojo Mathew Asst. Professor CSE Dept., NIE Mysuru.

2 Table of Contents 1. Simple Queue Implementation with arrays Circular queue with global container array,front & rear Circular queue using structure. No dynamic memory allocation Circular queue using structure & dynamic memory allocation for container...11

3 1. Simple Queue Implementation with arrays. #include<stdio.h> #define MAXSIZE 5 int items[maxsize]; int front = -1, rear = -1; // Initial empty state void insert(int value) if(rear == MAXSIZE-1) printf("\nqueue is Full!!"); else if(front == -1) front = 0; rear++; items[rear] = value; printf("\ninserted -> %d", value); void delete() if(front == -1) printf("\nqueue is Empty!!"); else printf("\ndeleted : %d", items[front]); front++; if(front > rear) front = rear = -1; void display() if(rear == -1) printf("\nqueue is Empty!!!"); else int i; printf("\nqueue elements are:\n"); for(i=front; i<=rear; i++) printf("%d\t",items[i]); int main() //delete is not possible on empty queue //insert 5 elements insert(1); insert(2);

4 insert(3); insert(4); insert(5); //6th element can't be added to queue because queue is full insert(6); //delete removes element entered first i.e. 1 //Now we have just 4 elements insert(6);

5 2. Circular queue with global container array,front & rear. #include <stdio.h> #define MAXSIZE 5 int items[maxsize]; int front = -1, rear =-1; int isfull() if( (front == rear + 1) (front == 0 && rear == MAXSIZE-1)) return 1; int isempty() if(front == -1) return 1; void insert(int element) if(isfull()) printf("\n Queue is full!! \n"); else if(front == -1) front = 0; rear = (rear + 1) % MAXSIZE; items[rear] = element; printf("\n Inserted -> %d", element); int delete() int element; if(isempty()) printf("\n Queue is empty!! \n"); return(-1); else element = items[front]; if (front == rear) /* Q has only one element, so we reset the queue after dequeing it. */ front = -1; rear = -1;

6 else front = (front + 1) % MAXSIZE; printf("\n Deleted element -> %d \n", element); return(element); void display() int i; if(isempty()) printf(" \n Empty Queue\n"); else printf("\n Front -> %d ",front); printf("\n Items -> "); for( i = front; i!=rear; i=(i+1)%maxsize) printf("%d ",items[i]); printf("%d ",items[i]); printf("\n Rear -> %d \n",rear); int main() // Fails because front = -1 insert(1); insert(2); insert(3); insert(4); insert(5); // Fails to insert because front == 0 && rear == MAXSIZE - 1 insert(6); insert(7); // Fails to insert because front == rear + 1

7 insert(8); insert(8); insert(9); insert(10);

8 3. Circular queue using structure. No dynamic memory allocation. #include <stdio.h> #define MAXSIZE 5 struct Queue int items[maxsize]; int front, rear; ; int isfull(struct Queue *cq) if( (cq->front == cq->rear + 1) (cq->front == 0 && cq->rear == MAXSIZE-1)) return 1; int isempty(struct Queue *cq) if(cq->front == -1) return 1; void insert(struct Queue *cq, int element) if(isfull(cq)) printf("\n Queue is full!! \n"); else if(cq->front == -1) cq->front = 0; cq->rear = (cq->rear + 1) % MAXSIZE; cq->items[cq->rear] = element; printf("\n Inserted -> %d", element); int delete(struct Queue *cq) int element; if(isempty(cq)) printf("\n Queue is empty!! \n"); return(-1); else element = cq->items[cq->front]; if (cq->front == cq->rear) cq->front = -1;

9 cq->rear = -1; /* Q has only one element, so we reset the queue after dequeing it.? */ else cq->front = (cq->front + 1) % MAXSIZE; printf("\n Deleted element -> %d \n", element); return(element); void display(struct Queue *cq) int i; if(isempty(cq)) printf(" \n Empty Queue\n"); else printf("\n Front -> %d ",cq->front); printf("\n Items -> "); for( i = cq->front; i!=cq->rear; i=(i+1)%maxsize) printf("%d ",cq->items[i]); printf("%d ",cq->items[i]); printf("\n Rear -> %d \n",cq->rear); int main() struct Queue q; q.front = q.rear = -1; // Fails because front = -1 insert(&q,1); insert(&q,2); insert(&q,3); insert(&q,4); insert(&q,5); // Fails to insert because front == 0 && rear == MAXSIZE - 1 insert(&q,6); insert(&q,7);

10 // Fails to insert because front == rear + 1 insert(&q,8); insert(&q,8); insert(&q,9); insert(&q,10);

11 4.Circular queue using structure & dynamic memory allocation for container. #include <stdio.h> #include <stdlib.h> #define MAXSIZE 5 struct Queue int *items; int front, rear; ; void initqueue(struct Queue *cq) cq->front = cq->rear = -1; void deinitqueue(struct Queue *cq) free(cq->items); int isfull(struct Queue *cq) if( (cq->front == cq->rear + 1) (cq->front == 0 && cq->rear == MAXSIZE-1)) return 1; int isempty(struct Queue *cq) if(cq->front == -1) return 1; void insert(struct Queue *cq, int element) if(isfull(cq)) printf("\n Queue is full!! \n"); else if(cq->front == -1) cq->front = 0; cq->rear = (cq->rear + 1) % MAXSIZE; cq->items[cq->rear] = element; printf("\n Inserted -> %d", element);

12 int delete(struct Queue *cq) int element; if(isempty(cq)) printf("\n Queue is empty!! \n"); return(-1); else element = cq->items[cq->front]; if (cq->front == cq->rear) cq->front = -1; cq->rear = -1; /* Q has only one element, so we reset the queue after dequeing it.? */ else cq->front = (cq->front + 1) % MAXSIZE; printf("\n Deleted element -> %d \n", element); return(element); void display(struct Queue *cq) int i; if(isempty(cq)) printf(" \n Empty Queue\n"); else printf("\n Front -> %d ",cq->front); printf("\n Items -> "); for( i = cq->front; i!=cq->rear; i=(i+1)%maxsize) printf("%d ",cq->items[i]); printf("%d ",cq->items[i]); printf("\n Rear -> %d \n",cq->rear); int main() struct Queue q; q.items = (int*)malloc(maxsize*sizeof(int)); initqueue(&q); // Fails because front = -1 insert(&q,1); insert(&q,2);

13 insert(&q,3); insert(&q,4); insert(&q,5); // Fails to insert because front == 0 && rear == MAXSIZE - 1 insert(&q,6); insert(&q,7); // Fails to insert because front == rear + 1 insert(&q,8); insert(&q,8); insert(&q,9); insert(&q,10); deinitqueue(&q);

Queue: Queue Representation: Basic Operations:

Queue: Queue Representation: Basic Operations: Queue: Queue is an abstract data structure, somewhat similar to Stacks. Unlike stacks, a queue is open at both its ends. One end is always used to insert data (enqueue) and the other is used to remove