Lecture Windows programming: Chapter 6 - Châu Thị Bảo Hà

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Lecture Windows programming: Chapter 6 - Châu Thị Bảo Hà

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Chapter 6 of lecture Windows programming introduce about Arrays - collections. In this chapter you will be learn contents: Declaring and Allocating arrays, initializing an array, properties – methods of an array, foreach loops, System.Collections namespace, ArrayList class,...

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Arrays Collections Chapter 6 Ebook: Beginning Visual C# 2010, part 1, chapter 5, 11 Reference: CSharp How to Program
Contents  Arrays  Collections Slide 2
Arrays (p.110)  Declaring and Allocating arrays  Initializing an array  Properties – Methods of an array  foreach loops  Array parameter  Multidimensional arrays Slide 3
Declaring and Allocating arrays  Arrays are indexed lists of variables stored in a single array type variable DataType[ ] ArrayName; // declare array ArrayName = new DataType[size]; // allocate array // declare and allocate array DataType[ ] ArrayName = new DataType[size]; Example: int[] a = new int[12]; bool[] b = new bool[100]; Circle[] listCir = new Circle[5]; // reference types  When arrays are allocated, the elements are initialized:  zero for the numeric data-type  false for bool variables  null for reference types Slide 4
Initializing an array  Arrays can be declared, allocated, initialized in a statement int[] myIntArray = new int[5] { 2, 4, 6, 8, 10};  Allocate space for the array – number of elements in initializer list determines the size of array int[] myIntArray = { 2, 4, 6, 8, 10}; Slide 5
Properties Methods of an array  array_name.Length  returns size of array  array_name.GetValue (int index)  array_name[int index]  returns an object at position index  array_name.SetValue (object value, int index)  array_name[int index] = value  modifies an object at position index Slide 6
foreach Loops foreach ( in ) { // can use for each element }  Example: int[] myArray = { 2, 4, 6, 8, string[] friendNames = { "Robert", "Mike", 10}; "Jeremy" }; foreach ( int x in myArray ) foreach (string friendName in friendNames) { Console.WriteLine( x ); Console.WriteLine( friendName ); Circle[] listC = new Circle[3] }{ new Circle(5.0), new Circle(7.0), new Circle(9.0) } foreach (Circle c in listC) { Console.WriteLine(c.Radius + " : " + c.getArea(); } Slide 7
Example string output = ""; const int ARRAY_SIZE = 10; int[] x = new int[ 10 ]; int[] y = { 32, 27, 64, 18, 95, 14, 90, 70, 60, 37 }; int[] z; z = new int[ ARRAY_SIZE ]; for ( int i = 0; i < z.Length; i++ ) z.SetValue(2 + 2 * i, i); output += "Subscript\tArray x\tArray y\tArray z\n"; for ( int i = 0; i < ARRAY_SIZE; i++ ) Change output += i + "\t" + x.GetValue(i) + "\t" + y.GetValue(i) + for to "\t" + z.GetValue(i) + "\n"; foreach loop? MessageBox.Show( output, "Initializing an array of int values", MessageBoxButtons.OK, MessageBoxIcon.Information ); Slide 8
Array parameter  No need the number of elements in the parameter array when you define the method  Example:  void InputArray (int[] a)  void OutputArray (int[] a)  int Sum (int[] arr)  bool Search (int[] arr, int key)  Pass arrays as arguments to methods by specifying the name of the array (no brackets)  Example: InputArray(a);  Arrays are passed by reference  Individual array elements are passed by value Slide 9
Array parameter: Example private void showOutputButton_Click( object sender, System.EventArgs e ) { int[] a = { 1, 2, 3, 4, 5 }; for ( int i = 0; i < a.Length; i++ ) outputLabel.Text += " " + a[ i ]; ModifyArray( a ); // passed by reference outputLabel.Text += "\n"; for ( int i = 0; i < a.Length; i++ ) outputLabel.Text += " " + a[ i ]; ModifyElement( a[ 3 ] ); outputLabel.Text += "\na[ 3 ] after ModifyElement: " + a[ 3 ]; } public void ModifyArray( int[] b ) { Slide
Multidimensional Arrays (p.113)  Require two or more subscripts to identify a particular element  Arrays that require two subscripts to identify an element are called double-subscripted arrays  rectangular arrays  often represent tables  jagged arrays (arrays of arrays)  arrays that compose jagged arrays can be of different lengths Slide
Rectangular arrays Column 0 Column Column 2 Column 3 1 Row 0 a[0, 0] a[0, 1] a[0, 2] a[0, 3] Row 1 a[1, 0] a[1, 1] a[1, 2] a[1, 3] Row 2 a[2, 0] a[2, 1] a[2, 2] a[2, 3] Column index (or subscript) Row index (or subscript) Array name Slide
Rectangular arrays (cont.)  Declaring – Allocating: DataType[,] ArrayName; ArrayName = new DataType [rowSize, colSize]; DataType[,] ArrayName = new DataType [rowSize, colSize];  Example: int[,] b = new int[ 2, 2 ]; b[ 0, 0 ] = 1; b[ 0, 1 ] = 2; b[ 1, 0 ] = 3; b[ 1, 1 ] = 4; or: int[,] b = { { 1, 2 }, { 3, 4 } };  GetLength (int x): returns size of xth dimension in a array Slide
Jagged arrays (arrays of arrays) Column 0 Column Column 2 Column 3 1 Row 0 a[0, 0] a[0, 1] a[0, 2] a[0, 3] Row 1 a[1, 0] a[1, 1] Row 2 a[2, 0] a[2, 1] a[2, 2] Column index (or subscript) Row index (or subscript) Array name Slide
Jagged arrays (cont.)  Declaring – Allocating: DataType[ ][ ] ArrayName; ArrayName = new DataType[Size][ ]; DataType[ ][ ] ArrayName = new DataType[Size][ ];  Example: int[ ][ ] c = new int[2][ ]; c[0] = new int[] { 1, 2 }; c[1] = new int[] { 3, 4, 5 };  Length property: returns number of rows or columns  c.Length  2  c[1] .Length  3 Slide
Rectangular arrays: Example Slide
Jagged arrays: Example Slide
Example Slide
Contents  Arrays  Collections Slide
Collection classes  Collection classes are used for maintaining lists of objects, and they may expose more functionality than simple arrays  Collection classes are defined as part of the System.Collections or System.Collections.Generic namespace  the collection classes in the System.Collections allow to create untyped collections  store any type of object in the collection  the collection classes in the System.Collections.Generic allow to create typed collections  only store the specified data type  the data type is specified in angle bracket () after name of the collection class Slide