Thread: Please check my C++

Originally Posted by matsp

By the way, here's a post I made a while back with regards to creating a menu system - perhaps you can use it as a base:
http://cboard.cprogramming.com/showp...6&postcount=18

--
Mats

I'm trying to understand your code, well, i've never worked on linked list but have an idea..

Code:

// Class menucontext
class menucontext 
{
public:
	bool fquit;
	menucontext() : fquit(false) {}
	~menucontext() {};
};
typedef void (*menufunc)(menucontext &ctxt);

Could you explain the purpose of this function pointer menufunc & class menucontext? Expanding to that, how/for what reasons it's used here in"domenu"?

Code:

		for(p = head; p; p = p->next) 
		{
			if (p->item->isChoice(c))
			{
				p->item->domenu(ctxt);
				choosen = true;
			}
		}

.............

void menuitem::domenu(menucontext &ctxt) 
{
	func(ctxt);
}

Originally Posted by matsp

The context is there so that you can have some data [that is not global] that you can pass between the function that uses the menu class itself, and the functions provided as the menu functions. This class probably would need to be expanded - right now it only contains a flat to indicate if we want to quit or not.

--
Mats

In simple terms, could you explain this for loop

Code:

		for(p = head; p; p = p->next) 
		{
			if (p->item->isChoice(c))
			{
				p->item->domenu(ctxt);
				choosen = true;
			}
		}

thnx

Originally Posted by matsp

In a linked list, you often only track the head and/or tail - the other components are held together with the links within the list. So, if we have 3 elements (1, 2, 3) in a linked list:
head->1->2->3 <- tail

So tail points to the currently last element in the list at the end of the function. When the first element is inserted, obviously the first AND the last element are the same one, so tail and head point to the same thing. Once we start adding more element, tail will point to the most recently added [since we don't do any sorting or such - elements are in the order they were inserted].

--
Mats

mind you the if/else you have is only used to point, not to insert... Maybe that's where my confusion was!

Originally Posted by matsp

Well, the "insert" in a linked list is just a "link it in", which is done in the else-part. In the initial link, there is nothing other than the head to "link in" - and the next link is NULL, which is already done above the if-else (since we ALWAYS insert at the end, next is always NULL on a new node). The else part sets the current tail's next pointer to the new node, then moves the tail to the new last element.
Insert element 3 in a 1, 2 list:

Code:

before:
head -> 1
        |
        v
tail -> 2
        |
        v
       NULL
after tail->next = node:
head -> 1
        |
        v
tail -> 2
        |
        v
        3
        |
        v
       NULL
after tail = node:
head -> 1
        |
        v
        2
        |
        v
tail -> 3
        |
        v
       NULL

--
Mats

makes sense, thanx...

Lastly on this topic...

This class (menucontext) probably would need to be expanded - right now it only contains a flag to indicate if we want to quit or not.

What do you imagine should be added as a member to this class... Say i have 5 Menu Items...

Originally Posted by matsp

It depends very much on how you want to design the user-interface for your system. I can imagine something like this for renting a car out:
* Register new hirer (or find existing).
* Find suitable car
* finalize contract

If we do it this way, when you register new hirer, you need to remember that hirer for when you finalize the contract. Likewise for the car. Once you have issued the contract, you probably want to "forget" what the current hirer and car is.

--
Mats

Am not sure if you understood me, take for example..

Code:

		case ADDCAR:	AddNewCar();	// Add new car
						break;
			
		case UPDATEF:	UpdateFleetFile();	// Save changes to text file
						break;
		
		case EDITF:		EditFleetContract();	// Edit contract details
						break;
		
		case DELCAR:	DeleteCar(); // Remove a specific car from fleet
						Pause();

This is what needs to be part of Menu, or currently is... But, the class 'menucontext' has fquit as the only functionality, to help quit the program. My question is how do i relate the above options/functionalities with this class, if at all. My knowledge is i have to pass all these functions above any many others using the addmenu() function, which inserts them to the list or table. So, where does menucontext come in? or of what help except 'Quitting' would it be! Hope am clear....

Originally Posted by matsp

If all you "need" from one menu to another is to know if you wanted to quit or not, then fQuit is all you need in menucontext. If on the other hand you would like to remember something from one menu selection to another (for example the car you select in "find car"), then you may want to add that to the menucontext.

--
Mats

mhh... notice menufunc() has menucontext as a ref parameter... How do i pass a function with a different parameter, and a none void return value? Let me guess, this is going back to what you said (modifying menucontext for all functions ) ... Well, let take one function ..

Code:

bool ShowFleetList(vector<car>::iterator i , bool status);

How would i cater for this?

Originally Posted by matsp

What do you currently pass to ShowFleetList? [that is, what does the code look like in the calling place].
Mats

Code:

FleetIterator iterate;
ShowFleetList(iterate=fleet.begin(), found);

only fleet is global...

If the vector of cars is a global, then you don't need to pass anything.

They may be other functions which receives parameters, and return values

If it's not a global, then you need some way to pass it along, and menucontext would be one way to achieve that.

one example would help, maybe based on the above function...