Queue

A Queue can be defined as a list of items.Queue follows the method of first in first out .

• First element inserted is first one retrieved
• Can’t retrieve elements from middle of queue or end of queue
• Can’t insert elements into middle or start of queue 

      

 Examples: Implement Enqueue And Dequeue Process By Using LinkedList

#include <stdio.h>
#include <stdlib.h>
#include <conio.h>
#define size 3

struct node {
    int data ;
    struct node *pnext;
};

struct node *phead;
struct node *ptail;
int count;
struct node *createnode(int data);
int equeue(int data);
int dequeue ();

struct node *createnode (int data){
    struct node *ptr=NULL;
    if(count<size){
        ptr=(struct node*) malloc(sizeof(struct node));
        if(ptr){
            count++;
            ptr->data=data;
            ptr->pnext=NULL;
        }
    }
    return ptr;
}

int enqueue(int data){
    int flag=0;
    struct node *ptr=createnode(data);
    if(ptr){
        flag=1;
        if (ptail==NULL){
            ptail=phead=ptr;
        }
        else
            ptail->pnext=ptr;
            ptail=ptr;
    }
    return flag;
}

int dequeue (){
    struct node *pcur=phead;
    int data;
    if(pcur){
        phead=phead->pnext;
        data=pcur->data;
        free(pcur);
        count--;

    }
    return data;
}

void printall (){
    struct node *pointer;
    pointer=phead;
    int i=0;
    for (i=0;i!=size;i++){
        printf("%d\n",pointer->data);
        pointer=pointer->pnext;
    }
}
int main()
{
    int input,output ;
    int stat;
    do{
        printf("You Want To\n 1-Enqueue\n 2-Dequeue\n 3-Print All\n");
        scanf("%d",&stat);
        switch(stat){
        case 1 :
            printf("Please Enter Input Integer Number:\n");
            scanf("%d",&input);
            enqueue(input);
            break;
        case 2 :
            output=dequeue();
            printf("%d\n",output);
            break;
        case 3 :
            printall();
            break;
        }
        printf("Do you want do something else ?(y/n)\n");
    }while(getch()=='y');

    return 0;
}

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