Thread: Menu problem involving structs

I am currently doing a Queue program a using structs and linked lists. Most of it works fine however the menu used to drive it keeps having runtime errors when i try to print the queue.
Am I doing something wrong?

functions

Code:

CTaxi_addTaxi(int TaxiReg)
{
	struct node *temp,*r;
	temp= (struct node *)malloc(sizeof(struct node));
	temp->data=TaxiReg;
	r=(struct node *)p;

	if (p == NULL)
	{
		p=temp;
		p->next =NULL;
	}
	else
	{
		while( r->next != NULL)
		r=r->next;
		r->next =temp;
		r=temp;
		r->next=NULL;
	}
}

CTaxiDelete(char taxi)
{
	struct node *temp, *m;
	temp=p;
	while(temp!=NULL)
	{
		if(temp->data==taxi)
		{
			if(temp==p)
			{
				p=temp->next;
				free(temp);
				return;
			}
			else
			{
				m->next=temp->next;
				free(temp);
				return;
			}
		}
		else
		{
			m=temp;
			temp= temp->next;
		}
	}
}

CTaxi_printQueue(struct node *r)
{
	r=p;
	if(r==NULL)
	{
		printf("Taxi Rank is currently empty!");
		return;
	}

	while(r!=NULL)
	{
		printf(" -> %d ",r->data);
		r=r->next;
	}
	printf("/n");
}

menu

Code:

main()
{
	int menuChoice = 0;
	p=NULL;
	while(menuChoice != 4)
	{
		printf("1.Add Taxi\n");
		printf("2.Delete Taxi\n");
		printf("3.Print current taxi queue\n");
		printf("4.Exit\n");
		printf("Enter a choice from the above menu:");
		scanf("%d",&menuChoice);
		
		switch(menuChoice)
		{
			case 1:
			{
				int TaxiReg;
				printf("Please enter a reg no :\n");
				scanf("%d",&TaxiReg);
				CTaxi_addTaxi(TaxiReg);
				break;
			}
			
			case 2:
			{
				int TaxiReg;
				printf("Please enter a reg no to delete :\n");
				scanf("%d",&TaxiReg);
				CTaxiDelete(TaxiReg);
				break;
			}
			
			case 3:
			{
				struct node *n;
				printf("The Current taxi queue is:\n");
				CTaxi_printQueue(n);
				break;
			}
			
			case 4:
			{
				menuChoice =4;
				return;
			}
		}
	}
}

Also is there a way to search for a specific node in the list? So if I wanted to find a particular taxi entered by the user it will display it.

Thanks for any help/suggestions given

Perhaps we need to see the "addQueue" function?

--
Mats

When dealing with a queue, it is much simpler to have two variables, one representing the "head" of the queue, and one for the "tail" (tail where things are entered, head is where things are taken off).

I'm sure someone else will spot it, but I can't actually see anything wrong with teh code.

--
Mats

Originally Posted by NyHoK

I have been staring at it for ages and can't figure it out. Any idea on how to implement searches on linked lists?

Something like this:

Code:

node *p;
for(p = head; p; p = p->next)
{
   if (p->member == what_you_search_for)
     break;
}
if (p) ... we found something.

There is no other way than to walk along the list and check each item.

--
Mats