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Queues, Stacks, and Dictionaries

This guide introduces three essential collection classes in C#: Queues, Stacks, and Dictionaries. Queues implement First In, First Out (FIFO) behavior, using methods like Enqueue to add and Dequeue to remove items. Stacks use Last In, First Out (LIFO) principles, utilizing Push to add and Pop to remove items. Dictionaries provide key-value pairs, allowing for non-consecutive keys and retrieval of objects by keys. Learn how to create and manage these collections and improve your programming skills with these impactful data structures.

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Queues, Stacks, and Dictionaries

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  1. Queues, Stacks, and Dictionaries

  2. More Collections • You have been introduced to arrays and Generic.Lists, as well as the Items collections of ListBoxes and ComboBoxes. • We will now introduce three more collection classes: Queues, Stacks, and Dictionaries. • Note that these are classes—to actually use them, you must create instance objects of them by calling their constructors (New).

  3. Queues • The Generic.Queue class enables you to create a collection of objects which model First In, First Out (FIFO) behavior. • To add an item to a Queue, you don’t use Add; you use Enqueue. • Enqueue basically means “Go to the end of the line”.

  4. Queues • To get the object that is at the front of the line, use Dequeue. • Dequeue both retrieves a reference to the object at the front of the line AND removes it from the Queue. • In the code below, the variable a will point to the object that was at the front of BankLine, and • That object (reference) will no longer be in the Queue. • See the “ListsQueuesStacksDictionaries” sample program for all of the code and a working example of a Queue.

  5. Queues and Stacks

  6. Stacks • Stack collections model LIFO behavior: Last In, First Out. • LIFO is generally thought of as a stack of dirty dishes—the last dish brought to the sink will be the first one washed. • Stacks use “Push” to add items: • Use “Pop” to remove items (LIFO) from the stack: • See the “ListsQueuesStacksDictionaries” sample program for all of the code and a working example of a Stack.

  7. Dictionaries • The Generic.Dictionary collection class is also very useful. • The Dictionary is like an array, in that every item in the collection has an index. • Unlike an array, however, the indices in Dictionary collections do not have to be consecutive numbers. • They can be any number, or even Strings. • These indices function just like primary keys; they provide a short code for locating items in the Dictionary.

  8. Creating a Dictionary and Adding Items • Note that you have to define two data types for a dictionary: the type of the key (index) and the type of object the dictionary contains. • Don’t forget to actually create the Dictionary object by calling New. • Items are added using Add, which takes two parameters: the key and the object.

  9. Retrieving Objects from a Dictionary • You retrieve items from a Dictionary by way of their keys. • In the code below, the user types in a suspected uniqname. • If the uniqname exists in the dictionary, the corresponding Student object is returned.

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