C Programming Help

Magnolia_Fan

Sorry for the annoyance again, this should more than likely be my last coding problem for a few months at least, you guys have been good to me in the past so I figured I'd give it a shot. I'm trying to create a Queue to store garage information : so far I've got this: -

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

struct queueNode { /* self-referential structure */
char data;
struct queueNode *nextPtr;
};

typedef struct queueNode QueueNode;
typedef QueueNode *QueueNodePtr;

/* function prototypes */
void printQueue( QueueNodePtr );
int isEmpty( QueueNodePtr );
char dequeue( QueueNodePtr *, QueueNodePtr * );
void enqueue( QueueNodePtr *, QueueNodePtr *, char );
void instructions( void );

int main()
{
char make[80];
char model[80];
int year;
float price;
char reg[80];
int mileage;

QueueNodePtr headPtr = NULL, tailPtr = NULL;
int choice;

instructions();
printf( "? " );
scanf( "%d", &choice );

while ( choice != 3 ) {

switch( choice ) {

case 1:
printf( "Enter a make: " );
scanf( "\n%s",make);


printf( "Enter a model: " );
scanf( "\n%s",model);


printf( "Enter a year: " );
scanf( "\n%i",&year);


printf( "Enter a price: " );
scanf( "\n%fl", &price);

printf( "Enter a car reg: " );
scanf( "\n%s", reg);


printf( "Enter a mileage: " );
scanf( "\n%i", &mileage);



enqueue( &headPtr, &tailPtr,make,model,year,price,reg,mileage);
printQueue( headPtr);
break;
case 2:
if ( !isEmpty( headPtr ) ) {
mileage = dequeue( &headPtr, &tailPtr );
printf( "%i has been dequeued.\n", mileage );
}

printQueue( headPtr );
break;

default:
printf( "Invalid choice.\n\n" );
instructions();
break;
}

printf( "? " );
scanf( "%d", &choice );
}

printf( "End of run.\n" );
return 0;
}

void instructions( void )
{
printf ( "Enter your choice:\n"
" 1 to add an item to the queue\n"
" 2 to remove an item from the queue\n"
" 3 to end\n" );
}

void enqueue( QueueNodePtr *headPtr, QueueNodePtr *tailPtr,char value )
{
QueueNodePtr newPtr;

newPtr = malloc( sizeof( QueueNode ) );

if ( newPtr != NULL ) {
newPtr->data = value;
newPtr->nextPtr = NULL;

if ( isEmpty( *headPtr ) )
*headPtr = newPtr;
else
( *tailPtr )->nextPtr = newPtr;

*tailPtr = newPtr;
}
else
printf( "%c not inserted. No memory available.\n",
value );
}

char dequeue( QueueNodePtr *headPtr, QueueNodePtr *tailPtr )
{
char value;
QueueNodePtr tempPtr;

value = ( *headPtr )->data;
tempPtr = *headPtr;
*headPtr = ( *headPtr )->nextPtr;

if ( *headPtr == NULL )
*tailPtr = NULL;

free( tempPtr );
return value;
}

int isEmpty( QueueNodePtr headPtr )
{
return headPtr == NULL;
}

void printQueue( QueueNodePtr currentPtr )
{
if ( currentPtr == NULL )
printf( "Queue is empty.\n\n" );
else {
printf( "The queue is:\n" );

while ( currentPtr != NULL ) {
printf( "%c --> ", currentPtr->data );
currentPtr = currentPtr->nextPtr;
}

printf( "NULL\n\n" );
}
}

I tried putting it into a structure and reading the structure but I kept getting errors, any help as usual would be greatly appreciated, Thanks

aidan_walsh

Ah, Christ, my eyes! Code tags, people! Especially for lengthy posts.

Magnolia_Fan

what do you mean by code tags, sorry...this is the second or third time I've posted such long code, I figured it could easily be copied and pasted into a word document and then into C

aidan_walsh

[ code] [ /code ]

Preserves the indentation, makes it easier to read.

Cake Fiend

Holy cow, that's a mess! My brain hurts from trying to understand that code.

OK, it looks like you're trying to program a simple database using a single-linked list (or Queue as you call it).

You need to have a good understanding of pointers before you go near linked lists - it doesn't look like you do.

There are way too many problems with this code to list out in one post, so I've attached a very basic database I programmed for you to look at (change the .txt extension to .c). My code has no buffer overrun protection in it, so bear that in mind (also remember never to do that yourself )

Post again if there is anything you don't understand in my code, or if there are things about yours that you still don't get. First and foremost though, make sure your pointer knowledge is up to scratch.

Magnolia_Fan

Is there anyway of doing it without using Files?

Cake Fiend

Yes, I only put in file i/o in there so that the database would be saved. Change 'head = read_data(head);' to 'head = NULL;' and remove 'write_data(head);' from the end of main() and it should completely bypass the file i/o functions. Apart from the reading on load and writing on exit, everything is done in RAM.

How are you getting on with it so far?

elivsvonchiaing

struct queueNode { /* self-referential structure */
char data;
/* should be char *data */
struct queueNode *nextPtr;
};
...
...

void enqueue( QueueNodePtr *headPtr, QueueNodePtr *tailPtr,char value )
/* should be void enqueue( QueueNodePtr *headPtr, QueueNodePtr *tailPtr,char *value ) */

{
QueueNodePtr newPtr;
++ char *buff;

newPtr = malloc( sizeof( QueueNode ) );
++ buff = malloc(strlen(value));
++ strcpy(buff, value);

if ( newPtr != NULL ) {
newPtr->data = buff;
....


Just what I spotted immediately - might be more probs though...

Magnolia_Fan

Well, I'll try that tommorow its a little late now, I took a look at your example today, its actually a helluva lot cooler than the way we do it in out tutorials but I think if I handed it up the lecturer may be upset. I was kind of caught up with a VB.Net project and neglected C for a while so my pointers ain't up to scratch. I tried tinkering with yours but of course I'd screw it up. But with your new instructions I'd say I should get it working.
P.S Hey Thanks alot guys, your always great help on this site...you'll get me passed my exams!