Array and ArrayList

1. Array and ArrayList ISYS 350

2. 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.

3. 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];

4. 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]

5. 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";

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

7. 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 (inti = 0; i <= myGPAs.Length - 1; ++i) { sumGPA += myGPAs[i]; } avgGPA = sumGPA / myGPAs.Length; MessageBox.Show("Average GPA is: " + avgGPA);

8. 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);

9. Create a Loan Payment Form

10. Data Binding: Binding an array to a control’sDataSource 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 listboxselectedIndex to access the rate: • intRate[listBox1.SelectedIndex]

11. 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"));

12. 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.

13. ArrayList Property and Methods • ArrayList • Count • Add • Clear

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

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

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

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

18. Binding an arrayList to a control:Control’s DataSource property • A string arrayList to store rates with “%”: • ArrayListstrRateList = 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: • ArrayListrateList = new ArrayList() { .03, .04, .05, .06, .07, .08 }; • Use listboxselectedIndex to access the rate: rate = (double)rateList[listBox1.SelectedIndex]; Note: Need the (double) cast operator.

19. 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"));