Use C language to explain deleting elements in the queue

A data structure is a collection of data organized in a structured manner. It is divided into two types as mentioned below -

• Linear Data Structure - Data is organized in a linear manner. For example, arrays, structures, stacks, queues, and linked lists.

• Nonlinear Data Structure - Data is organized in a hierarchical manner. For example, trees, graphs, sets, tables.

Queue

It is a linear data structure, insertion is done on the backend, and deletion is done on the frontend.

The order of the queue is FIFO – first in, first out

Operation

• Insert – Insert elements into the queue.
• Delete – Remove an element from the queue.

Conditions

• Queue overflow − Attempt to insert an element into a full queue.

• Queue is in streaming state − An attempt is made to remove an element from an empty queue.

Algorithm

Given below is the algorithm for inserting ( ) -

• Check for queue overflow.

if (r==n)
printf ("Queue overflow")

• Otherwise, insert an element into the queue.

q[r] = item
r++

gives the HTML code of a deletion algorithm:

Given below is an algorithm for deletion ( ) −

• Check for queue under flow.

if (f==r)
printf ("Queue under flow")

• Otherwise, remove an element from the queue.

item = q[f]
f++

The following is the algorithm of display ( ) -

• Check whether the queue is empty.

if (f==r)
printf("Queue is empty")

• Otherwise, print all elements from 'f' to 'r'.

for(i=f; i<r; i++)
printf ("%d", q[i]);

Program

The following is the C program for removing elements from the queue −

#include <stdio.h>
#define MAX 50
void insert();
int array[MAX];
int rear = - 1;
int front = - 1;
main(){
   int add_item;
   int choice;
   while (1){
      printf("1.Insert element to queue </p><p>");
      printf("2.Delete an element from queue</p><p>");
      printf("3.Display elements of queue </p><p>");
      printf("4.Quit </p><p>");
      printf("Enter your choice : ");
      scanf("%d", &choice);
      switch (choice){
         case 1:
            insert();
         break;
         case 2:
            delete();
         case 3:
            display();
         break;
         case 4:
            exit(1);
         default:
         printf("Wrong choice </p><p>");
      }
   }
}
void insert(){
   int add_item;
   if (rear == MAX - 1)
      printf("Queue Overflow </p><p>");
   else{
      if (front == - 1)
      /*If queue is initially empty */
      front = 0;
      printf("Inset the element in queue : ");
      scanf("%d", &add_item);
      rear = rear + 1;
      array[rear] = add_item;
   }
}
void display(){
   int i;
   if (front == - 1)
      printf("Queue is empty </p><p>");
   else{
      printf("Queue is : </p><p>");
      for (i = front; i <= rear; i++)
         printf("%d ", array[i]);
         printf("</p><p>");
   }
}
void delete(){
   if (front == - 1 || front > rear){
      printf("Queue Underflow </p><p>");
      return ;
   }
   else{
      printf("Element deleted from queue is : %d</p><p>",array[front]);
      front = front + 1;
   }
}

Output

When executing the above program, the following results will be produced -

1.Insert element to queue
2.Delete an element from queue
3.Display elements of queue
4.Quit
Enter your choice: 1
Inset the element in queue: 12
1.Insert element to queue
2.Delete an element from queue
3.Display elements of queue
4.Quit
Enter your choice: 1
Inset the element in queue: 23
1.Insert element to queue
2.Delete an element from queue
3.Display elements of queue
4.Quit
Enter your choice: 1
Inset the element in queue: 34
1.Insert element to queue
2.Delete an element from queue
3.Display elements of queue
4.Quit
Enter your choice: 2
Element deleted from queue is: 12
Queue is:
23 34
1.Insert element to queue
2.Delete an element from queue
3.Display elements of queue
4.Quit
Enter your choice: 2
Element deleted from queue is: 23
Queue is:
34
1.Insert element to queue
2.Delete an element from queue
3.Display elements of queue
4.Quit
Enter your choice: 4

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