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Queue Operations in C++
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| # Queue | ||
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| ## What is Queue ? | ||
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| A **queue** is basically a linked list where data can be **inserted** into it only from the **rear end** and can be **deleted** from the **front end**. | ||
| A queue is a _first in first out_(**FIFO**) structure. The queue implementation needs to keep a track of front and rear ends of the queue. | ||
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| <div align="center"> | ||
| <img src = "https://user-images.githubusercontent.com/76544476/136729206-69bf88f3-79f9-4c6d-ba8b-13f06be9c904.png" width="500" height="300"> | ||
| </div> | ||
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| <p align=center> Fig:1 | ||
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| ## Queue Operations | ||
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| There are 4 operations in queue and they are listed below: | ||
| - Enqueue | ||
| - Dequeue | ||
| - Queue front | ||
| - Queue rear <br> | ||
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| ### Enqueue | ||
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| Insertion of data/element into queue is known as **Enqueue**. Once the data have been inserted, the new elements will be in the rear end of queue. | ||
| If there is no more of space/room for another element to be inserted, then the queue is in **Overflow** condition. | ||
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| <div align="center"> | ||
| <img src = "https://user-images.githubusercontent.com/76544476/136730297-db0af07b-c2dd-4efb-92ed-2290de523b24.png" width="400" height="400"> | ||
| </div> | ||
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| <p align=center> Fig:2 | ||
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| ### Dequeue | ||
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| Deletion of data/element from queue is known as**Dequeue**. Data at the front of queue can be removed and returned to the user from the queue. | ||
| If there are no data in the queue already and if dequeue is aimed, then the queue is in **Underflow** condition. | ||
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| <div align="center"> | ||
| <img src = "https://user-images.githubusercontent.com/76544476/136732398-e98a90fe-22a4-4383-af69-6bc27f14e982.png" width="400" height="400"> | ||
| </div> | ||
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| <p align=center> Fig:3 | ||
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| ### Queue Front | ||
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| Retrieval of data from the front of the queue is done with **Queue Front**. | ||
| If there is no data present in the queue and when the queue front is attemped, then the queue is in **Underflow** condition. | ||
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| <div align="center"> | ||
| <img src = "https://user-images.githubusercontent.com/76544476/136823803-91a956e0-2abc-4115-82a3-85cf59018962.png" width="400" height="400"> | ||
| </div> | ||
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| <p align=center> Fig:4 | ||
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| ### Queue Rear | ||
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| Retrieval of data from the rear of the queue is done with **Queue Rear**. | ||
| If there is no data present in the rear and when the queue rear is attemped, then the queue is in **Underflow** condition. | ||
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| <div align="center"> | ||
| <img src = "https://user-images.githubusercontent.com/76544476/136824321-8df1e01c-7e76-494d-a0a5-27190869a6c0.png" width="400" height="300"> | ||
| </div> | ||
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| <p align=center> Fig:5 | ||
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| ### Program Demonstration: | ||
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| ```Cpp | ||
| #include <iostream> | ||
| using namespace std; | ||
| void enqueue(int [],int &,int &,int,int); | ||
| void dequeue(int [],int &,int &); | ||
| void queueFront(int [],int &); | ||
| void queueRear(int [],int &); | ||
| void display(int [],int &,int &); | ||
| int main() | ||
| { | ||
| int queue[100],front=-1,rear=-1,n,x,key,choice; | ||
| int result; | ||
| char c; | ||
| cout<<"Enter the size of queue :"<<endl; | ||
| cin>>n; | ||
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| do { | ||
| cout << "MENU:1.Enqueue 2.Dequeue 3.Display queue 4.Display queue front 5. Display queue rear\n"; | ||
| cin >> choice; | ||
| switch (choice) | ||
| { | ||
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| case 1:cout << "Enter the element for insertion: "; | ||
| cin >> x; | ||
| enqueue(queue, front, rear,x,n); | ||
| break; | ||
| case 2:dequeue(queue, front, rear); | ||
| break; | ||
| case 3:display(queue, front, rear); | ||
| break; | ||
| case 4:queueFront(queue, front); | ||
| break; | ||
| case 5:queueRear(queue, rear); | ||
| break; | ||
| } | ||
| cout << "press 'y' if you want to continue: "; | ||
| cin >> c; | ||
| } while (c == 'y'); | ||
| } | ||
| void enqueue(int queue[],int &f,int &r,int x,int s) | ||
| { | ||
| if(r>=s-1) | ||
| cout<<"Queue Overflow"<<endl; | ||
| else | ||
| { | ||
| r++; | ||
| queue[r]=x; | ||
| if(f==-1) | ||
| { | ||
| f++; | ||
| } | ||
| } | ||
| } | ||
| void dequeue(int queue[],int &f,int &r) | ||
| { | ||
| int x; | ||
| if(f==-1) | ||
| cout<<"Queue Underflow"<<endl; | ||
| else | ||
| { | ||
| x=queue[f]; | ||
| if(f==r) | ||
| { | ||
| f=r=-1; | ||
| } | ||
| else | ||
| { | ||
| f++; | ||
| } | ||
| } | ||
| cout<<x<<" Deleted from Queue"<<endl; | ||
| } | ||
| void queueFront(int queue[],int &f) | ||
| { | ||
| cout<<"The front element is "<<queue[f]<<endl; | ||
| } | ||
| void queueRear(int queue[],int &r) | ||
| { | ||
| cout<<"The Rear element is "<<queue[r]<<endl; | ||
| } | ||
| void display(int queue[],int &f,int &r) | ||
| { | ||
| if(f==-1) | ||
| cout<<"QUEUE IS EMPTY"<<endl; | ||
| else | ||
| { | ||
| for(int i=f;i<=r;i++) | ||
| { | ||
| cout<<queue[i]<<" "; | ||
| }cout<<endl; | ||
| } | ||
| } | ||
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| ``` | ||
| ### Output: | ||
| > Enter the size of queue : <br> | ||
| > 3 <br> | ||
| > MENU:1.Enqueue 2.Dequeue 3.Display queue 4.Display queue front 5. Display queue rear <br> | ||
| > 1 <br> | ||
| > Enter the element for insertion: 10 <br> | ||
| > press 'y' if you want to continue: y <br> | ||
| > MENU:1.Enqueue 2.Dequeue 3.Display queue 4.Display queue front 5. Display queue rear <br> | ||
| > 1 <br> | ||
| > Enter the element for insertion: 20 <br> | ||
| > press 'y' if you want to continue: y <br> | ||
| > MENU:1.Enqueue 2.Dequeue 3.Display queue 4.Display queue front 5. Display queue rear <br> | ||
| > 1 <br> | ||
| > Enter the element for insertion: 30 <br> | ||
| > press 'y' if you want to continue: y <br> | ||
| > MENU:1.Enqueue 2.Dequeue 3.Display queue 4.Display queue front 5. Display queue rear <br> | ||
| > 3 <br> | ||
| > 10 20 30 <br> | ||
| > press 'y' if you want to continue: y <br> | ||
| > MENU:1.Enqueue 2.Dequeue 3.Display queue 4.Display queue front 5. Display queue rear <br> | ||
| > 4 <br> | ||
| > The front element is 10 <br> | ||
| > press 'y' if you want to continue: y <br> | ||
| > MENU:1.Enqueue 2.Dequeue 3.Display queue 4.Display queue front 5. Display queue rear <br> | ||
| > 5 <br> | ||
| > The Rear element is 30 <br> | ||
| > press 'y' if you want to continue: y <br> | ||
| > MENU:1.Enqueue 2.Dequeue 3.Display queue 4.Display queue front 5. Display queue rear <br> | ||
| > 2 <br> | ||
| > 10 Deleted from Queue <br> | ||
| > press 'y' if you want to continue: y <br> | ||
| > MENU:1.Enqueue 2.Dequeue 3.Display queue 4.Display queue front 5. Display queue rear <br> | ||
| > 3 <br> | ||
| > 20 30 <br> | ||
| > press 'y' if you want to continue: n <br> | ||
| #### Source: | ||
| Fig:1 | ||
| [Slidetodoc](https://slidetodoc.com/15-3-stacks-a-stack-is-a-linear/) | ||
| <br> | ||
| Fig:2 | ||
| [Programiz](https://www.programiz.com/dsa/circular-queue) | ||
| <br> | ||
| Fig:3 | ||
| [Stackexchange](https://tex.stackexchange.com/questions/489987/how-to-draw-stack-and-queue-data-structure) | ||
| <br> | ||
| Fig:4 | ||
| [Hackerearth](https://www.hackerearth.com/practice/data-structures/queues/basics-of-queues/tutorial/) | ||
| <br> | ||
| Fig:5 | ||
| [Javapoint](https://www.javatpoint.com/array-representation-of-queue) | ||
| <br> |
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| - [Queue](https://github.com/ishrutik/winter-of-contributing/blob/C_CPP/C_CPP/Data%20Structures/Queue/Queue%20Implementation/readme.md)<br> | ||
| - [Queue using Arrays](https://github.com/ishrutik/winter-of-contributing/blob/C_CPP/C_CPP/Data%20Structures/Queue/Queue%20Implementation/Queue_Using_Array.cpp)<br> | ||
| - [Queue using linked list](https://github.com/ishrutik/winter-of-contributing/blob/C_CPP/C_CPP/Data%20Structures/Queue/Queue%20Implementation/Queue_Using_LL.cpp) | ||
| - [Queue Operations](Queue-Operations.md) | ||
| - [Implementation of queue using stack](./implementation_of_queue_using_stack.md) | ||
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