Download Array and ArrayList

Array
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 double[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
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
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
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]);
}
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
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;
}
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]
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");