queue.c

/* Corrected  19/3/90 - nolonger leaves queue in memory!     */
/* Note UNIX would clear the dynamically allocated memory    */
/* when the program ends                                     */
/*							     */
/* queue.c 						     */
/* Demo of dynamic data structures in C                      */

#include <stdio.h>

#define FALSE 0
#define NULL 0

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

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);
    }
}