Implements queue as a linked list.

C: Program that implements queue as a linked list.

#include <stdio.h>
#include <conio.h>

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

struct queue
{
    struct node *front ;
    struct node *rear ;
} ;

void initqueue ( struct queue * ) ;
void addq ( struct queue *, int ) ;
int delq ( struct queue * ) ;
void delqueue ( struct queue * ) ;

void main( )
{
    struct queue a ;
    int i ;

    clrscr( ) ;

    initqueue ( &a ) ;

    addq ( &a, 11 ) ;
    addq ( &a, -8 ) ;
    addq ( &a, 23 ) ;
    addq ( &a, 19 ) ;
    addq ( &a, 15 ) ;
    addq ( &a, 16 ) ;
    addq ( &a, 28 ) ;

    i = delq ( &a ) ;
    printf ( "\nItem extracted: %d", i ) ;

    i = delq ( &a ) ;
    printf ( "\nItem extracted: %d", i ) ;

    i = delq ( &a ) ;
    printf ( "\nItem extracted: %d", i ) ;

    delqueue ( &a ) ;

    getch( ) ;
}

/* initialises data member */
void initqueue ( struct queue *q )
{
    q -> front = q -> rear = NULL ;
}

/* adds an element to the queue */
void addq ( struct queue *q, int item )
{
    struct node *temp ;

    temp = ( struct node * ) malloc ( sizeof ( struct node ) ) ;
    if ( temp == NULL )
        printf ( "\nQueue is full." ) ;

    temp -> data = item ;
    temp -> link = NULL ;

    if ( q -> front == NULL )
    {
        q -> rear = q -> front = temp ;
        return ;
    }

    q -> rear -> link = temp ;
    q -> rear = q -> rear -> link ;
}

/* removes an element from the queue */
int delq ( struct queue * q )
{
    struct node *temp ;
    int item ;

    if ( q -> front == NULL )
    {
        printf ( "\nQueue is empty." ) ;
        return NULL ;
    }

    item = q -> front  -> data ;
    temp = q -> front ;
    q -> front = q -> front -> link ;
    free ( temp ) ;
    return item ;
}

/* deallocates memory */
void delqueue ( struct queue *q )
{
    struct node *temp ;

    if ( q -> front == NULL )
        return ;

    while ( q -> front != NULL )
    {
        temp = q -> front ;
        q -> front = q -> front -> link ;
        free ( temp ) ;
    }
}