Array and ArrayList 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); 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()); }

DataBinding and parallel arrayList Must add this reference: – using System.Collections; Declare arrayList with initial values – Ex: ArrayList strRateList = new ArrayList() { "3%", "4%", "5%", "6%", "7%", "8%" }; ArrayList rateList = new ArrayList() {.03,.04,.05,.06,.07,.08 }; New element can be added: – strRateList.Add("9%"); – rateList.Add(.09); Number of elements: – rateList.Count

Binding an arrayList to a control: Control’s DataSource property A string arrayList to store rates with “%”: – ArrayList strRateList = new ArrayList() { "3%", "4%", "5%", "6%", "7%", "8%" }; Bind the array to a listbox: – listBox1.DataSource = strRateList; A parallel arrayList to store the numerical rates: – ArrayList rateList = new ArrayList() {.03,.04,.05,.06,.07,.08 }; Use listbox selectedIndex to access the rate: rate = (double)rateList[listBox1.SelectedIndex]; Note: Need the (double) cast operator.

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