Array, ArrayList and List ISYS 350

Array An array allows you to store a group of items of the same type together. Processing a large number of items in an array is easier than processing a large number of items stored in separate variables.

Declaring a Array Declare an array in one statement: – Type[] arrayName = new type[array size]; – Ex: string[]empName = new string[3]; double[] intRate = new intRate[6];

Array Elements Array elements are indexed from 0 to array size – 1. Each element can be accessed by its index: – arrayName[index] – Ex: empName[0] intRate[2]

Array Initialization With the declaration statement: – string[] empName = new string[3] { "Peter", "Paul", "Mary" }; – double[] intRate = new double[6] {.03,.04,.05,.06,.07,.08 }; Initialize each element separately: – empName[0] = "Peter"; – empName[1] = "Paul"; – empName[2] = "Mary";

Accessing Array Elements with a for loop Using array’s Length property: int arrayIndex; for (arrayIndex = 0; arrayIndex <= 2; ++arrayIndex) { MessageBox.Show(empName[arrayIndex].ToString()); } for (arrayIndex = 0; arrayIndex <= empName.Length-1; ++arrayIndex) { MessageBox.Show(empName[arrayIndex].ToString()); } Note: Length - 1

Example: Compute the sum and average of numbers in an array double[] myGPAs = new double[5] { 2.5, 3.2, 3.4, 2.9, 3.6 }; double sumGPA=0, avgGPA; for (int i = 0; i <= myGPAs.Length - 1; ++i) { sumGPA += myGPAs[i]; } avgGPA = sumGPA / myGPAs.Length; MessageBox.Show("Average GPA is: " + avgGPA);

Using Array’s Methods and Length property Sum(), Average(), Max(), Min(); double[] myGPAs = new double[5] { 2.5, 3.2, 3.4, 2.9, 3.6 }; double avgGPA, maxGPA, minGPA; avgGPA = myGPAs.Average(); maxGPA = myGPAs.Max(); minGPA=myGPAs.Min(); MessageBox.Show(“The size of array is: " + myGPAs.Length);

Create a Loan Payment Form

Data Binding: Binding an array to a control’s DataSource property A string array to store rates with “%”: – string[] strRate = new string[6] { "3%", "4%", "5%", "6%", "7%", "8%" }; Bind the array to a listbox: – listBox1.DataSource = strRate; A parallel array to store the numerical rates: – double[] intRate = new double[6] {.03,.04,.05,.06,.07,.08 }; Use listbox selectedIndex to access the rate: – intRate[listBox1.SelectedIndex]

Code Example double loan, rate, term, payment; loan = double.Parse(textBox1.Text); rate = intRate[listBox1.SelectedIndex]; if (radioButton1.Checked) term = 15; else term = 30; payment = Financial.Pmt(rate / 12, term * 12, -loan); MessageBox.Show(payment.ToString("c"));

ArrayList An arrayList allows you to store a group of objects together. Objects stored in an arraylist may not be the same type of object. ArrayList resizes dynamically. As elements are added, it grows in capacity to accommodate them. Numerical data stored in an arrayList needs to be casted.

ArrayList Property and Methods ArrayList – Count – Add – Clear

Declaring an arrayList: 1. Must add this reference: using System.Collections; 2. The Data Type of ArrayList Members Can Be Different ArrayList demoArrayList = new ArrayList(); int myInt = 10; double myDouble = 12.34; string myString = "Hello"; demoArrayList.Add(myInt); demoArrayList.Add(myDouble); demoArrayList.Add(myString); demoArrayList.Add(textBox1); demoArrayList.Add(button1); for (int i = 0; i < demoArrayList.Count; i++) { MessageBox.Show(demoArrayList[i].GetType().ToString()); }

foreach Loop The foreach statement repeats a group of embedded statements for each element in an array or each object in an arrayList

foreach loop example foreach (object x in demoArrayList) { MessageBox.Show(x.GetType().ToString()); MessageBox.Show(x.ToString()); }

List Class Represents a strongly typed list of objects that can be accessed by index. Objects stored in a list must be the same type of object. – A list of type T objects List resizes dynamically as arraylist.

List Property and Methods List – Count – Add – Clear

Example Adding three invisible textboxes to a form with background color of Green, Yellow and Red. Declaring a List containing the 3 textboxes. Use a timer’s click event to show the textboxes in rotation.

List myBox = new List (); private void Form14_Load(object sender, EventArgs e) { myBox.Add(textBox1); myBox.Add(textBox2); myBox.Add(textBox3); } int i=0,j; private void timer1_Tick(object sender, EventArgs e) { j = i % 3; for (int k = 0; k < myBox.Count;k++ ) { if (k == j) myBox[k].Visible = true; else myBox[k].Visible = false; } i++; }