Chapter 5 Arrays - Collections

Properties - Methods of an array returns size of array  array_name.. GetValue int index  array_name[ int index]  returns an object at position index  array_name.. SetValue object

Arrays - Collections

Chapter 5

Ebook: Beginning Visual C# 2010, part 1, chapter 5, 11

 Arrays

 Collection classes

Declaring and Allocating arrays

int[] a;

a = new int[12];

string[] b = new string[100];

double[] array1 = new double[10], array2 = new double[20];

 When arrays are allocated, the elements are initialized:

 zero for the numeric data-type

 false for bool variables

 null for reference types

ArrayName = new DataType [size]; // allocate array

// declare and allocate array

DataType [ ] ArrayName = new DataType [size];

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};

foreach Loops

 Example:

foreach ( <baseType> <var_name> in

<array> ) {

// can use <var_name> for each element }

Properties - Methods of an array

 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

string output = "" ;

const int ARRAY_SIZE = 10 ;

int [] y = { 32 , 27 , 64 , 18 , 95 , 14 , 90 , 70 , 60 , 37 };

int [] z;

z = new int [ ARRAY_SIZE ];

"\t" + z.GetValue(i) + "\n" ;

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

Array parameter: Example

private void showOutputButton_Click( object sender, System.EventArgs e )

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

Rectangular arrays

Row 0 Row 1 Row 2

Column 1

Column 0 Column 2 Column 3

a[0, 0] a[0, 1] a[0, 2] a[0, 3]

a[1, 0] a[1, 1] a[1, 2] a[1, 3]

a[2, 0] a[2, 2] a[2, 3]

Column index (or subscript) Row index (or subscript) Array name

a[2, 1]

Rectangular arrays (cont.)

 GetLength (int x): returns size of xth dimension in a array

 GetLength(0)  returns number of rows

 GetLength(1)  returns number of columns

DataType[,] ArrayName;

ArrayName = new DataType [rowSize, colSize];

DataType[,] ArrayName = new DataType [rowSize, colSize];

Jagged Arrays (Arrays of arrays)

Row 0 Row 1 Row 2

Column 1

Column 0 Column 2 Column 3

a[0, 0] a[0, 1] a[0, 2] a[0, 3]

a[1, 0] a[1, 1]

a[2, 0] a[2, 2]

Column index (or subscript) Row index (or subscript) Array name

a[2, 1]

Jagged Arrays (cont.)

ArrayName = new DataType [Size][ ];

DataType[ ][ ] ArrayName = new DataType [Size][ ];

Example: Rectangular arrays

Example: Jagged Arrays

Example

 Arrays

 Collection classes

Collection classes

 Collection classes in general are used for

maintaining lists of objects, and they may expose more functionality than simple arrays

 Some class in System.Collections namespace:

 ArrayList

 Hashtable

 Queue

 Stack

ArrayList: Properties-Methods

value) Inserts an object at the index

ArrayList; otherwise, returns false

the specified object

ArrayList: Example

static void Main() {

ArrayList intArray = new ArrayList ();

Random r = new Random ();

// thêm phần tử vào ArrayList

for ( int i = 0; i < 5; i++) {

Example: Defining Collections

Student

- id: String

- name: String

- address: String+ ToString(): String

Students

- list: ArrayList<Student>

+ Add( st: Student ) : bool+ Remove( id: String) : bool+ ToString(): String

1 0 *

 Why Hashtable?

 Suppose you have some data, which needs to

be stored in two dimensional array and have

a link format of Key and Value

 For example, a person name and his social

security number and we can access there

data using a key

Key Value

Hashtable: Properties-Methods

Add (object key , object

value ) Adds an object to the Hashtable with the specified key and value into the

Hashtable

Values Gets an ICollection of all the values

stored in the Hashtable

stored in the Hashtable

Remove (object obj ) Removes the first occurrence of the

object

Count Gets the number of elements

Clear() Removes all the elements

Hashtable: Properties-Methods

Contains (object item ) Returns true if the specified object

is in the Hashtable; otherwise, returns false

ContainsKey(object key ) Determines whether the

Hashtable contains a specific key

ContainsValue(object

value ) Determines whether the Hashtable contains a specific value

hashTable [object key ] Gets the value with specified key

Hashtable: Code examples

 Create new hashtable:

Hashtable exampleTable = new Hashtable();

 Adding elements to the table:

Hashtable: Gets all data

 If you want to get all keys or values of Hashtable

 If you want to get all keys and values of Hashtable

IDictionaryEnumerator enumerator = simpleTable.GetEnumerator();

Example 1

static void Main()

{

// tạo hashtable

Hashtable hashTable = new Hashtable ();

hashTable.Add(“00440123”, ”Ngoc Thao”);

hashTable.Add(“00123001”, ”My Tien”);

hashTable.Add(“00330124”, ”Thanh Tung”);

// truy cập qua Item

Console.WriteLine(“ Gia tri tai khoa 00440123 la: {0} ”,

hashTable[“00440123”]);

}

Example 2

static void Main()

{

// tạo hashtable

Hashtable hashTable = new Hashtable ();

hashTable.Add(“ 00440123 ”,” Ngoc Thao ”);