Implementation of Queues

1. Implementation using Array (Static Queue)
2. Implementation using Linked List (Dynamic Queue)

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Structure of Queue

Structure of Queue.

#define max 5
struct queue
{
	int data[max];
	int front, rear ;
}

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Algorithm for Insertion in Queue

Insert ( )
1. If (REAR == N) Then [Check for overflow]
2.		Print: Overflow
3. Else
4.		If (FRONT and REAR == 0) Then [Check if QUEUE is empty]
			(a) Set FRONT = 1
			(b) Set REAR = 1
5. 			Else
6. 				Set REAR = REAR + 1 [Increment REAR by 1]
			[End of Step 4 If]
7. 			QUEUE[REAR] = ITEM
8. 			Print: ITEM inserted
	[End of Step 1 If]
9.	Exit

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Algorithm for Deletion in Queue

Delete ( )
1. If (FRONT == 0) Then [Check for underflow]
2. 		Print: Underflow
3. Else
4. 		ITEM = QUEUE[FRONT]
5. 		If (FRONT == REAR) Then [Check if only one element is left]
			(a) Set FRONT = 0
			(b) Set REAR = 0
6. 		Else
7. 			Set FRONT = FRONT + 1 [Increment FRONT by 1]
		[End of Step 5 If]
8. 		Print: ITEM deleted
	[End of Step 1 If]
9. Exit

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Array implementation of Queue

In this type of implementation we use array structure for data storage.

#include<stdio.h>
#include<conio.h>
#define SIZE 5

int front=-1;
int rear=-1;
int q[SIZE];

void insert();
void del();
void display();

void main()
{
	int choice;
	clrscr();
	do
	{
		clrscr();
		printf("\t Menu");
		printf("\n 1. Insert");
		printf("\n 2. Delete");
		printf("\n 3. Display ");
		printf("\n 4. Exit");

		printf("\n Enter Your Choice:");
		scanf("%d",&choice);

		switch(choice)
		{
			case 1:
				insert();
				display();
				getch();
				break;
			case 2:
				 del();
				 display();
				 getch();
				 break;
			case 3:
				display();
				getch();
				break;
			case 4:
				printf("End of Program....!!!!");
				getch();
				exit(0);
		}
	}while(choice!=4);
}

void insert()
{
	int no;
	printf("\n Enter No.:");
	scanf("%d",&no);

	if(rear < SIZE-1)
	{
		q[++rear]=no;
		if(front==-1)
		front=0;// front=front+1;
	}
	else
	{
		printf("\n Queue overflow");
	}
}

void del()
{
	if(front==-1)
	{
		printf("\nQueue Underflow");
		return;
	}
	else
	{
		printf("\nDeleted Item:-->%d\n",q[front]);
	}
	if(front==rear)
	{
		front=-1;
		rear=-1;
	}
	else
	{
		front=front+1;
	}
}

void display()
{
	int i;
	if(front==-1)
	{
		printf("\nQueue is empty....");
		return;
	}
	for(i=front;i<=rear;i++)
		printf("\t%d",q[i]);
}

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