01 - Queue using Array

Basic Logic

Queue Structure: The queue is a data structure where elements are added at the back and removed from the front.

Pointers:

• head points to the first element in the queue (front).
• tail points to the next available position for insertion (back).
• The head is incremented after each removal, and tail is incremented after each insertion.

Variables

• int n: Size of the queue.
• int head = -1, tail = -1: Initialize the head and tail pointers to indicate an empty queue.
• stack[n]: Array of integers or characters used as the queue.
• ele: The value to be added to the queue (enqueue operation).
• ch: Integer variable used to store the user’s choice for queue operations.

Implementation Logic

Global Variables:

• Declare n, head = -1, and tail = -1 globally to manage the queue.
• Functions for queue operations (enque, deque, and display) are declared, all of which return void.

Input Handling:

• In the main() function, the size of the queue is taken as input (scanf("%d", &n)).
• Declare stack[n] to store the queue elements and ele for input values of relevant type.

• A while(1) loop used to continuously display options and perform chosen operation.
• Declare int ch to hold the choice of user.
• make if else conditions for each function, an exit and miss typed number.
• Only option for enque needs to be passed the value to be added with stack

Function Logic

enque:

• Checks if the queue is full (tail == n-1).
• If not full, it increments tail and inserts the element into stack[tail].
• If head is -1 (first insertion), it increments head to indicate that the queue is no longer empty. dequ:
• Removal happens at the head, so check if (head == -1 || head > tail) which means queue is empty
• If not empty, it removes the element at head and increments head. display:
• Checks if the queue is empty (head == -1 || head > tail).
• If not empty, it displays all elements from head to tail.

• run a for loop with i = front and running till i <= tail with i++
• Print each stack[i]

Implementation

#include <stdio.h>
#include <stdlib.h>

int n, head = -1, tail = -1;

void enqu(int stack[], int x);
void dequ(int stack[]);
void display(int stack[]);

void main()
{
	printf("Enter the size of the Queue \n");
	scanf("%d", &n);
	int stack[n], ele;

	while(1)
	{
		int ch;
		printf("Make a choise:\n");
		printf("\n0.Exit\t1.Enqueue\n2.Dequeue\t3.Display\n");
		scanf("%d", &ch);
		
		if (ch == 0)
			exit(0);
		else if (ch == 1)
		{
			printf("\nProvide the Number to Add: \n");
			scanf("%d", &ele);
			enqu(stack, ele);
		}
		else if (ch == 2)
			dequ(stack);
		else if (ch == 3)
			display(stack);
		else
			printf("Enter a Proper choice\n");
	}
}

void enqu(int stack[], int x)
{
	if ( tail == n-1)
	{
		printf("\nThe Queue is Full\n");
	}
	else
	{
		if ( head == -1)
			head++;
		tail++;
		stack[tail] = x;
		printf("\nNumber %d has been inserted in the Queue\n\n", x);	
	}
}
void dequ(int stack[])
{
	if ( head == -1 || head > tail)
		printf("\nThe Queue is empty\n");
	else
	{
		printf("The Number %d has been removed\n", stack[head]);
		head++;
	}
}
void display(int stack[])
{
	if ( head == -1 || head > tail)
		printf("\nThe Queue is empty\n");
	else
	{
		printf("The Elements in the Queue are: \n");
		for( int i = head; i <= tail; i++)
		{
			printf("%d \t", stack[i]);
		}
		printf("\n");
	}
}