Working With C# Arrays And .NET Lists

1. Working With C# Arrays And .NET Lists

2. Lecture Overview • Discuss arrays • Discuss the various types of lists available through C# and the .NET Framework

3. Arrays (Introduction) • Arrays store repeating data items having the same data type • Arrays have one or more dimensions • The number of dimensions is called the rank • Think of a one-dimensional array as a list or vector • And a two-dimensional array as a table or grid • And a three-dimensional array as a cube

4. Arrays (Introduction 2) • Arrays are reference types • Memory is allocated from the managed heap • Uninitialized arrays will throw null reference exceptions if you try to use them • Test whether an array references null if (DemoArray1 == null) { // It’s a null pointer. }

5. Arrays (Introduction 3) • Arrays (almost always) have a lower bound (smallest subscript) of 0 • We can trick .NET to create non-zero-based arrays but DON’T DO IT • ReDim (Visual Basic) statement changes the size of an array while an application is running • It’s not supported in C# • We need to use Array.CopyToRefer to frmMain.btnCopyArray_Click

6. Declaring Arrays (Introduction) • The process is conceptually similar to VB • The syntax varies considerably though • The public and private access modifiers apply as usual • The [] characters follow the data type to denote that the variable is an array • The array name follows the data type • Example to declare an uninitialized array: private int[] demo;

7. Declaring 1D Arrays • Declare a one-dimensional array with no initial elements private int[] Alist; • Declare a one-dimensional array with 3 elements (subscripts values are 0 through 2) private int[] Alist = new int[3]; • Declare a one-dimensional array and initialize it private int[] Alist = new int[] {1, 2, 3};

8. Declaring 2D Arrays • Same as a 1D array but a comma (,) appears in the [] characters to mark 2 dimensions • Declare a two-dimensional array with no initial elements (unitialized) private int[,] A2DList[,]; • Declare an initialized two-dimensional array with 3 elements in each dimension private int[,] A2DList = new int[3,3];

9. Initializing 2D Arrays • Use nested initializers • Row is the innermost • Column is outermost • http://msdn.microsoft.com/en-us/library/2yd9wwz4.aspx Row 1 Row 2 Row 3 Col 2

10. Declaring 3D Arrays • Declare a three-dimensional array with 8 (2*2*2) elements private int[,,] A3DList = new int[1,1,1];

11. Determining Array Bounds • GetUpperBound and GetLowerBound get the largest and smallest subscript of an array dimension • An array’s lower bound is always 0 • The functions accept one argument, the 0-based dimension from which you want to get the upper or lower bound

12. Determining Array Bounds (Example) • Get the lower and upper bound of a one-dimensional array int[] Demo = new int[] {1, 2, 3, 4, 5, 6} System.Console.WriteLine( Demo.GetLowerBound(0)) System.Console.WriteLine( Demo.GetUpperBound(0))

13. Subscripts • You store and retrieve elements to and from an array via a subscript • The subscript value must be within the array bounds or an exception will be thrown • The number of subscripts used to reference a cell is the same as the arrays rank • One subscript for 1 dimension • Two subscripts for 2 dimensions

14. Referencing Array Members • Declare a 1-dimensional array and store a value in the 0th element private int[] i = new int[] { 1, 2, 3 }; i[0] = 3 ; • Declare a 2-dimensional array and store a value in the centerelement (row 1, column 1) TTTState[,] A2DArray = new TTTState[3,3]; A2DArray[1,1] = TTTState.X;

15. Examining an Array • We typically work with arrays using a loop (For loop) • Example intCurrentIndex; for (CurrentIndex = 0, DemoArray1.GetUpperBound(0), CurrentIndex++) { txtDemoArray1.AppendText(DemoArray1[CurrentIndex].ToString()); } Refer to frmMain.csPrintArray1

16. Arrays (Characteristics 2) • Arrays work like collections in that they can be enumerated using a foreach loop • If the array has multiple dimensions, each element will be examined in row-wise order foreach(int Current in DemoArray1) { txtDemoArray1.AppendText( _ Current.ToString() + “\n”) } Next Refer to frmMain.csPrintArray1 and btnInitializeArray

17. Arrays (Informational Members) • GetLength returns the number of elements in a particular dimension • Length gets the number of elements in all dimensions • GetUpperBound gets the largest subscript in a dimension • GetLowerBound get the smallest subscript in a dimension • Note that support has been added for arrays with Long subscripts

18. Copying Array Elements (1) • Arrays are reference types so assignment statements assign array references rather than copying elements • Use the CopyTo method to copy the element data

19. Copying Array Elements (2) • Call the CopyTo method on the source array as in MyArray.CopyTo • The first argument contains the destination array • The second argument contains the starting index in the destination array where elements will be copied • The destination array must have enough room to copy store the copied elements

20. Array.CopyTo (Example) • Copy DemoArray1 to DemoArray2 (We assume 1-dimensional arrays) • Note the array is initialized using dynamic value rather than a constant integer DemoArray2 = new double[DemoArray1.GetUpperBound(0)]; DemoArray1.CopyTo(DemoArray2, 0)

21. Arrays (Sorting) • The Sort method sorts all or part of an array in ascending order • Pass the array as the first argument • The second argument contains the starting index • The third argument contains the number of elements • The Reverse method reverses the order of the array’s elements

22. Arrays (Sorting – Example) • Sort arrays named DemoArray1 and DemoArray2 System.Array.Sort(DemoArray1) System.Array.Sort(DemoArray2)

23. Arrays (Reinitializing) • The Clear method reinitializes array elements • The first argument contains the array to clear • The second argument contains the starting subscript • The third argument contains the number of elements • Note the array’s size is not changed

24. Arrays (Reinitializing – Example) • Clear (reinitialize) the array named DemoArray1 System.Array.Clear( _ DemoArray1, 0, DemoArray1.Length())

25. Arrays (Finding Elements) • The IndexOf method searches an array for a particular value • The first argument contains the array to search • The second argument contains the search value • The optional third argument contains the index of the element where the search will begin • The method returns the index if the element is found or -1 if the element is not found Refer to frmMain.csbtnFind_Click

26. Arrays (Finding Elements) Refer to frmMain.vbbtnFind_Click double Value; int Index; Value = ToDouble(txtValue.Text); Index = System.Array.IndexOf(DemoArray1, Value); if (Index == -1) { txtDemoArray1.AppendText("Value not found"); } else { txtDemoArray1.AppendText("Value found at index “ + Index.ToString()); }

27. Collections (Introduction) • All lists are considered collections • Each collection references multiple objects (typically of the same type) • Collections are reference types • Each collection shares common members used to work with the collection • Indexer, add, …

28. Collections (Important Note) • Collections are categorized into two types • Older collections (System.Collections) store references having a data type of System.Object • Generic collections are strongly typed (System.Collections.Generic) • We will talk about each in turn

29. Collection Namespaces

30. Collections (Enumeration) • In this context, we mean examining the items in a list (NOT REFERRING TO enum) • Enumeration is provided by implementing the IEnumerable and IEnumerator interfaces • MSDN Interface link • http://msdn.microsoft.com/en-us/library/vstudio/ms173156.aspx

31. Collections (Enumeration) • IEnumeratorprovides forward-only navigation, and interfaces • IEnumerableprovides the enumerator itself • Their members are not explicitly called • They are called by the for each loop itself

32. Collections and Lists • IEnumerableprovides the functionality to enumerate a list • ICollection adds functionality (Add, Count Remove,Contains) • IList provides access by index or key

33. Collections and Lists

34. Collection / Array Relationship • The C# array declaration syntax is special • Array class implements IList but hides the add and remove members

35. Working with Collections • Common members • Countproperty returns the number of elements in the collection • Count property is 1-based • Clearmethod removes all of the elements from the collection • ToArraymethod converts the elements in a collection into an array • ToStringmethod returns a String representing the collection’s objects

36. Collections (The Short List) • The ArrayList maintains a list and is similar to an array • The SortedList class is very flexible and keeps items sorted • Use the Dictionary class to keep track of key/value pairs • There are others SortedDictionary, LinkedList, HashSet

37. The ArrayList Class (Introduction) • It’s possible to manage the list by adding, updating, and removing elements • It’s possible to find elements in the list • The size of an ArrayList grows dynamically • There is no need to redimension the list

38. The ArrayList Class (Members) • Call Add to add an item to the end of the list and Insert to add an item at a specific position • Call Remove or RemoveAt to remove an item • Call Clear to remove all items • Count and Capacity return the number of items and the number of possible (allocated) items

39. The ArrayList Class (Adding Items) • The Add method accepts one argument – the object to add • The item is added to the end of the list • The Insert method accepts two arguments • The first contains the positional index • The second contains the object to add

40. The ArrayList Class (Add Example) • Add a Student to the ArrayList Student s; S.RNumber = System.Convert.ToInt32(txtRNumber.Text); S.LastName = txtLastName.Text; S.FirstName = txtFirstName.Text; S.GPA = System.Convert.ToDouble(txtGPA.Text); StudentArrayList.Add(S);

41. The ArrayList Class (Insert Example) • Insert an item at a particular position int Pos = n; Student S; S.RNumber = System.Convert.ToInt32(txtRNumber.Text); S.LastName = txtLastName.Text; S.FirstName = txtFirstName.Text; S.GPA = System.Convert.ToDouble(txtGPA.Text); StudentArrayList.Insert(Pos, S);

42. The ArrayList Class (Removing an Item) • Call RemoveAt with the index of the item to remove • Example StudentArrayList.RemoveAt(CurrentIndex);

43. The ArrayList Class (Enumerating) • Use a foreach loop to enumerate each element in an ArrayList • A for loop can be used but is more cumbersome foreach(object CurrentStudent In StudentArrayList) { Console.WriteLine( ((Student) CurrentStudent).RNumber.ToString()); // Other Fields }

44. The SortedList Class (Introduction) • The SortedList operates similar to an ArrayList but the elements remain sorted • Internally, two parallel arrays are maintained • One for the keys • A second for the corresponding values • The SortedList class can become very slow so beware • Each addition or deletion requires that the indexes be updated.

45. Adding Items to a SortedList • The Add method adds an item to a SortedList • The first argument contains the key • An exception will be thrown if the key value is a duplicate • The second argument contains the data • It can be any object • Example assuming that “S” has a data type of Student CurrentSortedList.Add(“1234”,S);

46. Getting an Item from a SortedList • It works like an array • The key is passed as an argument to the list as follows: • Example: Student S; S.LastName = txtSLLastName.Text; S.FirstName = txtSLFirstName.Text; S.GPA = System.Convert.ToDouble(txtSLGPA.Text); StudentSortedList.[txtRNumber.Text] = S

47. Removing an Item from a SortedList • The Remove method accepts one argument, a reference to the key to remove • The method removes the item based on the key rather than the ordinal index value • The method returns True or False depending on whether the item was removed • Example • CurrentList.Remove(“Joe”);

48. Enumerating a SortedList • The enumerator (foreach loop) returns an element of type Dictionary • A dictionary has a key and a value • The values are returned in sorted order by key

49. Enumerating a SortedList (Example) • Enumerate the sorted list named StudentSortedList Student CurrentStudent; Foreach (System.Collections.Dictionary de in StudentSortedList) { CurrentStudent = (Student) de.Value; // Statements to process the current // student }

50. Other SortedList Methods • GetByIndex – Gets the record at the ordinal index value • IndexOfKey – Gets the index of a record based on a particular key