7 – Arrays

Lingma AchesonDepartment of Computer and Information Science, IUPUI

CSCI N331 VB .NET Programming

Represent A List of Values• Sometimes we need to represent a list

of values that have the similar characteristics.

• Example 1: Quarterly sales figures of one year. We can use four variables to store them.

dblQuarter1 = 12.8dblQuarter2 = 15.6dblQuarter3 = 23.2dblQuarter4 = 18.8

2

• Example 2: Names of the products that a vending machine carries. We can use six variables if there are six of them.

strName1 = “Pepsi”strName2 = “Sprite”strName3 = “Root Beer”strName4 = “Diet Coke”strName5 = “Mountain Dew”strName6 = “7 up”

3

Represent A List of Values

• Example 3: Exam scores of each student in a class. If there are 28 students in the class, do we need 28 variables? Is there a better way?

intScore1 = 97intScore2 = 68intScore3 = 82intScore4 = 91intScore5 = 85intScore6 = 88intScore7 = 72….

4

Represent A List of Values

What is an array?• Yes, use an array!• Array - A data structure that holds a list

of values of the same type. E.g.– Quarterly sales, an array of 4 values of type Double:

– Student scores, an array of 28 values of type Integer:

– Name of products in a vending machine, an array of 6 values of type String:

5

12.8 15.6 23.2 18.8

97 68 82 91 85 88 72 73 … 88

Coke Sprite Root Beer

Diet Coke

Mountain Dew

7 up

What is an array?• Caution – each structure is just one

variable! That variable can hold multiple values.

• E.g.– Quarterly sales:

Name of the array: QuarterlySales

How many values does the array have: 4

Type of the values: Double– Name of products in a vending machine

Name of the array: Products

How many values does the array have: 6

Type of the values: String6

12.8 15.6 23.2 18.8

Coke Sprite Root Beer

Diet Coke

Mountain Dew

7 up

Values in an Array• Now we have a name for the whole

structure, how do we refer to each value? E.g. how do I know the sales figure for the third quarter?

• Answer: Use position to identify a value as array values are stored in order. – E.g. QuarterlySales:

1st element of QuarterlySales: 12.8

2nd element of QuarterlySales: 15.6

3rd element of QuaterlySales: 23.2

4th element of QuarterlySales: 18.8

7

12.8 15.6 23.2 18.8

Values in an Array• How do we use VB code to specify a

position? Use array indexes that start from 0.E.g. QuarterlySales(0): 12.8

QuarterlySales(1): 15.6

QuarterlySales(2): 23.2

QuarterlySales(3): 18.8

E.g.‘Initialize all the values to 0

For n = 0 To 3

QuarterlySales(n) = 0

Next8

12.8 15.6 23.2 18.8

How to create an array?• Basic structure:

Dim arrayname As datatype()or:Dim arrayname() As datatypeE.g. ‘delare an array called dblQuarterlySales that holds Double valuesDim dblQuarterlySales As Double()

9

How to create an array?• Variations

‘declare an array with 3 as upperbound index.‘an array of 4 elements.Dim dblQuarterlySales As Double(3)

‘initialize values when declaring the array, no need to specify a size, as four values indicate a size of 4Dim dblQuarterlySales As Double() = {12.8, 15.6, 23.2, 18.8}

10

Retrieve Values from an Array• E.g

‘get the first element from the array and assign it to ‘a variabledblQuarterOne = dblQuarterlySales(0)

‘display result in a textboxtxtOutput.Text = “Last quarter sale: “ & _

Cstr(dblQuarterlySales(3))

‘display all the values in a listboxFor n = 0 To 3

lstOutput.Items.Add(Cstr(dblQuarteylySales(n)))

Next

11