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

8. foreach Loop
The foreach statement repeats a group of embedded statements for each element in an array.

9. foreach loop example
double[] myGPAs = new double[5] { 2.5, 3.2, 3.4, 2.9, 3.6 };
double sumGPA = 0, avgGPA;
foreach (int i in myGPAs) {
sumGPA += i; }
avgGPA = sumGPA / myGPAs.Length;
MessageBox.Show("Average GPA is: " + avgGPA);

10. 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);

11. Create a Loan Payment Form

12. If rates are stored in an array
Method 1: Using a loop to create the Listbox with rates in the Form Load event
string[] strRate = new string[6] { "3%", "4%", "5%", "6%", "7%", "8%" };
for(int i=0;i<=strRate.Length-1;i++) {
listBox1.Items.Add(strRate[i]); }

13. Method 2: 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;
Using the Form Load event

14. Data Binding Example
private void Form1_Load(object sender, EventArgs e) {
string[] strRate = new string[6] { "3%", "4%", "5%", "6%", "7%", "8%" };
listBox1.DataSource = strRate; }

15. Parallel Array Example
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]

16. Code Example
double[] intRate = new double[6] { .03, .04, .05, .06, .07, .08 };
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);
textBox2.Text = payment.ToString("c");

17. Sort an Array Array Class: Sort Method Example:
Sort array elements in increasing order
Example:
Array.Sort(myGPAs);

18. Exercise: Weighted Avg of three exams= 60%. highest score +30%
Exercise: Weighted Avg of three exams= 60%*highest score +30%*2nd highest score +10%*lowest score
Method 1: You may sort the array of exam scores. Or
Method 2: You may use the Max, Min and Sum functions.

19. Count the number of words in a textbox
string.Split() returns an array:

20. Count words example String myText = textBox1.Text;
string[] wordList = (myText.Split(default(string[]), StringSplitOptions.RemoveEmptyEntries));
textBox2.Text = wordList.Length.ToString();
foreach (string s in wordList) {
MessageBox.Show(s.ToString()); }

21. List<T> 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
A list of int, srting, etc.
List resizes dynamically, no need to declare size.

22. List Property and Methods
Count
Add
Clear

23. Example List<int> myInts = new List<int>(); myInts.Add(5);
MessageBox.Show(myInts.Count.ToString());

24. foreach Loop List<int> myInts = new List<int>();
myInts.Add(5);
myInts.Add(10);
myInts.Add(11);
MessageBox.Show(myInts.Count.ToString());
int sum = 0;
foreach(int i in myInts) {
MessageBox.Show(i.ToString());
sum += i; }
MessageBox.Show(sum.ToString());