/* Note UNIX would clear the dynamically allocated memory    */
/* when the program ends                                     */
/*                                                           */
/* queue.c                                                   */
/* Demo of dynamic data structures in C                      */


#include <stdio.h>
#include <ctype.h>
#include <stdlib.h>

#define FALSE 0
#define NULL 0

typedef struct  listelement {
    int     dataitem;
    struct listelement *link;
}   ;

void Menu (int *choice);
listelement * AddItem (listelement * listpointer, int data);
listelement * RemoveItem (listelement * listpointer);
void PrintQueue (listelement * listpointer);
void ClearQueue (listelement * listpointer);

main () {
    listelement listmember, *listpointer;
    int     data,
            choice;

    listpointer = NULL;
    do {
        Menu (&choice);
        switch (choice) {
            case 1: 
                printf ("Enter data item value to add  ");
                scanf ("%d", &data);
                listpointer = AddItem (listpointer, data);
                break;
            case 2: 
                if (listpointer == NULL)
                    printf ("Queue empty!\n");
                else
                    listpointer = RemoveItem (listpointer);
                break;
            case 3: 
                PrintQueue (listpointer);
                break;

            case 4: 
                break;

            default: 
                printf ("Invalid menu choice - try again\n");
                break;
        }
    } while (choice != 4);
    ClearQueue (listpointer);
}                               /* main */

void Menu (int *choice) {

    char    local;

    printf ("\nEnter\t1 to add item,\n\t2 to remove item\n\
\t3 to print queue\n\t4 to quit\n");
    do {
        local = getchar ();
        if ((isdigit (local) == FALSE) && (local != '\n')) {
            printf ("\nyou must enter an integer.\n");
            printf ("Enter 1 to add, 2 to remove, 3 to print, 4 to quit\n");
        }
    } while (isdigit ((unsigned char) local) == FALSE);
    *choice = (int) local - '0';
}

listelement * AddItem (listelement * listpointer, int data) {

    listelement * lp = listpointer;

    if (listpointer != NULL) {
        while (listpointer -> link != NULL)
            listpointer = listpointer -> link;
        listpointer -> link = (struct listelement  *) malloc (sizeof (listelement));
        listpointer = listpointer -> link;
        listpointer -> link = NULL;
        listpointer -> dataitem = data;
        return lp;
    }
    else {
        listpointer = (struct listelement  *) malloc (sizeof (listelement));
        listpointer -> link = NULL;
        listpointer -> dataitem = data;
        return listpointer;
    }
}

listelement * RemoveItem (listelement * listpointer) {

    listelement * tempp;
    printf ("Element removed is %d\n", listpointer -> dataitem);
    tempp = listpointer -> link;
    free (listpointer);
    return tempp;
}

void PrintQueue (listelement * listpointer) {

    if (listpointer == NULL)
        printf ("queue is empty!\n");
    else
        while (listpointer != NULL) {
            printf ("%d\t", listpointer -> dataitem);
            listpointer = listpointer -> link;
        }
    printf ("\n");
}

void ClearQueue (listelement * listpointer) {

    while (listpointer != NULL) {
        listpointer = RemoveItem (listpointer);
    }
}