Data structure is collection of data organized in a structured way. It is divided into two types as explained below −
Linear data structure − Data is organized in a linear fashion. For example, arrays, structures, stacks, queues, linked lists.
Nonlinear data structure − Data is organized in a hierarchical way. For example, Trees, graphs, sets, tables.
Queue
It is a linear data structure, where the insertion is done at rear end and the deletion is done at the front end.
The order of queue is FIFO – First In First Out
Operations
- Insert – Inserting an element into a queue.
- Delete – Deleting an element from the queue.
Conditions
Queue over flow − Trying to insert an element into a full queue.
Queue under flow − Trying to delete an element from an empty queue.
Algorithms
Given below is an algorithm for insertion ( ) −
- Check for queue overflow.
if (r==n)
printf ("Queue overflow")- Otherwise, insert an element in to the queue.
q[r] = item r++
Given below is an algorithm for deletion ( ) −
- Check for queue under flow.
if (f==r)
printf ("Queue under flow")- Otherwise, delete an element from the queue.
item = q[f] f++
Given below is an algorithm for display ( ) −
- Check whether the queue is empty or not.
if (f==r)
printf("Queue is empty")- Otherwise, print all the elements from ‘f’ to ‘r’.
for(i=f; i<r; i++)
printf ("%d", q[i]);Program
Following is the C program for deleting an element in 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 \n");
printf("2.Delete an element from queue\n");
printf("3.Display elements of queue \n");
printf("4.Quit \n");
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 \n");
}
}
}
void insert(){
int add_item;
if (rear == MAX - 1)
printf("Queue Overflow \n");
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 \n");
else{
printf("Queue is : \n");
for (i = front; i <= rear; i++)
printf("%d ", array[i]);
printf("\n");
}
}
void delete(){
if (front == - 1 || front > rear){
printf("Queue Underflow \n");
return ;
}
else{
printf("Element deleted from queue is : %d\n",array[front]);
front = front + 1;
}
}Output
When the above program is executed, it produces the following result −
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