A queue in C is basically a linear data structure to store and manipulate the data elements. It follows the order of First In First Out (FIFO).
In queues, the first element entered into the array is the first element to be removed from the array
A queue is open at both ends. One end is provided for the insertion of data and the other end for the deletion of data.
A queue can be implemented with any programming language such as C, Java, Python, etc.
Operations Associated with a Queue in C
A queue being an Abstract Data Structure provides the following operations for manipulation on the data elements:
isEmpty(): To check if the queue is empty
isFull(): To check whether the queue is full or not
dequeue(): Removes the element from the frontal side of the queue
enqueue(): It inserts elements to the end of the queue
Front: Pointer element responsible for fetching the first element from the queue
Rear: Pointer element responsible for fetching the last element from the queue
Working of Queue Data Structure
Queue follows the First-In-First-Out pattern. The first element is the first to be pulled out from the list of elements.
Front and Rear pointers keep the record of the first and last element in the queue.
At first, we need to initialize the queue by setting Front = -1 and Rear = -1
In order to insert the element (enqueue), we need to check whether the queue is already full i.e. check the condition for Overflow. If the queue is not full, we’ll have to increment the value of the Rear index by 1 and place the element at the position of the Rear pointer variable. When we get to insert the first element in the queue, we need to set the value of Front to 0.
In order to remove the element (dequeue) from the queue, we need to check whether the queue is already empty i.e. check the condition for Underflow. If the queue is not empty, we’ll have to remove and return the element at the position of the Front pointer, and then increment the Front index value by
When we get to remove the last element from the queue, we will have to set the values of the Front and Rear index to -1.
Implementation of Queue in C
Queues in C can be implemented using Arrays, Lists, Structures, etc. Below here we have implemented queues using Arrays in C.
#include <stdio.h># define SIZE 100
void enqueue();
void dequeue();
void show();
int inp_arr[SIZE];
int Rear = - 1;
int Front = - 1;
main()
{
int ch;
while (1)
{
printf("1.Enqueue Operation\n");
printf("2.Dequeue Operation\n");
printf("3.Display the Queue\n");
printf("4.Exit\n");
printf("Enter your choice of operations : ");
scanf("%d", &ch);
switch (ch)
{
case 1:
enqueue();
break;
case 2:
dequeue();
break;
case 3:
show();
break;
case 4:
exit(0);
default:
printf("Incorrect choice \n");
}
}
}
void enqueue()
{
int insert_item;
if (Rear == SIZE - 1)
printf("Overflow \n");
else
{
if (Front == - 1)
Front = 0;
printf("Element to be inserted in the Queue\n : ");
scanf("%d", &insert_item);
Rear = Rear + 1;
inp_arr[Rear] = insert_item;
}
}
void dequeue()
{
if (Front == - 1 || Front > Rear)
{
printf("Underflow \n");
return ;
}
else
{
printf("Element deleted from the Queue: %d\n", inp_arr[Front]);
Front = Front + 1;
}
}
void show()
{
if (Front == - 1)
printf("Empty Queue \n");
else
{
printf("Queue: \n");
for (int i = Front; i <= Rear; i++)
printf("%d ", inp_arr[i]);
printf("\n");
}
}
Output
1.Enqueue Operation
2.Dequeue Operation
3.Display the Queue
4.Exit
Enter your choice of operations : 1
Element to be inserted in the Queue: 10
1.Enqueue Operation
2.Dequeue Operation
3.Display the Queue
4.Exit
Enter your choice of operations : 1
Element to be inserted in the Queue: 20
1.Enqueue Operation
2.Dequeue Operation
3.Display the Queue
4.Exit
Enter your choice of operations : 3
Queue:
10 20
1.Enqueue Operation
2.Dequeue Operation
3.Display the Queue
4.Exit
Enter your choice of operations : 2
Element deleted from the Queue: 10
1.Enqueue Operation
2.Dequeue Operation
3.Display the Queue
4.Exit
Enter your choice of operations: 3
Queue:
20
