Source Code : Program that implements queue as a linked list.

 _{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 ) ;}

  _}

_}