Program that implements queue as a linked list.

#include
#include

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 ) ;
}
}