Post on 18-Dec-2015
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
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• 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”
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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….
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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:
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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
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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
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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()
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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}
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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
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