1 chapter 11 one-dimensional arrays. 2 chapter 11 topics l atomic and composite data types l...
TRANSCRIPT
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Chapter 11
One-Dimensional Arrays
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Chapter 11 Topics
Atomic and composite data types Declaring and instantiating an array The length of an array Manipulating the elements in an array Using an array to count frequencies Passing an array to a method
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VB .NET Data TypesVB .NET Data Types
Reference
Array Interface Class
primitive
Integral Boolean
Byte Char Short Integer Long Single Double
Floating Point
VB .NET Data Types
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11.1 Scalar Data Type
A scalar data type is a type in which
the values are ordered and each value is atomic (indivisible(不可分割 ))
Integer, Single, Double and Char data types are scalar.
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Declare variables to store and total 3 blood pressures
Dim bp0, bp1, bp2 As Integer
Dim total As Integer
bp1bp0 bp2
Total = bp0 + bp1 + bp2
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11.2 Composite Data Type
A composite data type(複合資料型態 ) is a type that
allows a collection of values to be associated with an identifier of that type.
In VB .NET, composite types are either classes, interfaces, or arrays.
There are 2 forms of composite types: unstructured and structured.
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Structured Data Type(結構化 )
A structured data type is a type which
is an organized collection of components; and allows individual components to be stored and retrieved.
The organization determines the method used to access individual components.
An array is a structured data type whose components are accessed by position.
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What if you wanted to store and total 1000 values?
Dim value(1000) As Integer
' declares and instantiates (creates)
' an array of 1000 int values
' and initializes all 1000 elements to zero
value(0) value(1) value(2) . . . . value(999)
0 0 0 . . . . 0
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11.3 Arrays(陣列 )
Arrays are data structures(資料結構 ) consisting of related data items all of the same type(相同資料型態 ).
An array type is a reference type. Contiguous memory locations(連續記憶體位置 ) are allocated for the array, beginning at the base address of the array.
A particular element in the array is accessed by using the array name together with the position of the desired element in square brackets. The position is called the index or subscript(索引 ).
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angle
Dim angle(4) As Single
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Dim angle(4) As Single
angle ( 0)
angle ( 1) angle ( 2 )
angle ( 3 )
angle
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Array Definition
An array is a collection of elements, all of the same data type(相同資料型態 ), given a single name.
The subscript (or index) must have an integral value. In VB .NET, the first array element always has subscript 0. The second array element has subscript 1, etc.
When allocated, the elements are automatically initialized to 0 for numeric primitive data type values, to False for Boolean variables, or to Nothing for references (non-primitive type values).
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Another Example
Declare and instantiate an array called angle to hold 4 individual double values.
Dim angle ( 4 ) As Single
' declares and allocates memory
angle(0) angle(1) angle(2) angle(3)
number of elements in the array
indexes or subscripts
0.0 0.0 0.0 0.0
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Using an initializer list in a declaration
Dim age( ) As Integer = { 23, 10, 16, 37, 12}
Dim i As Integer
For i = 0 to ages.Length – 1
Console.WriteLine("age("& i & ") = "& age(i) )Next i
age(0) age(1) age(2) age(3) age(4)
23 10 16 37 12
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Dim ArrayName(Int Expression) As DataType
Declaring and Allocating an Array
An array can be declared and allocated memory in one statement or an array can be declared in one statement and another statement ca be written later to allocate memory for the array, using Redim
SYNTAX FORMS
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Assigning values to individual array elements
Dim angle(4) As Single ' creates arrayDim m As Integer = 3angle(0) = 4.93angle(1) = -15.2angle(2) = 0.5angle(3) = 1.67angle(m) = angle (3) – 1.2
angle(0) angle(1) angle(2) angle(3)
4.93 -15.2 0.5 1.67
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Exmples
angle(2) = 9.6
angle(2) = CDlb(inFile.ReadLine())
outFile.WriteLine(angle(2))
y = Math.Sqrt(angle(2))
x = 6.8 * angle(2) + 7.5
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What values are assigned?
Dim temps (4) As Double ' allocates array
Dim m As Integer
For m = 0 To temps.Length – 1
temps(m) = 100.0 + m * 0.2
Next
temps(0) temps(1) temps(2) temps(3) temps(4)
? ? ? ? ?
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What values are assigned?
Dim temps (4) As Double ' allocates array
Dim m As Integer
For m = 0 To temps.Length – 1
temps(m) = 100.0 + m * 0.2
Next
temps(0) temps(1) temps(2) temps(3) temps(4)
? ? ? ? ?
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Now what values are printed?
Const ARRAY_SIZE As Integer = 5 ' named constantDim temps( ) As DoubleRedim temps(ARRAY_SIZE)Dim m As Integer
For m = temps.Length – 1 To 0 Step –1Console.WriteLine ("temps(“ & m & ") = " & temps(m))
temps(0) temps(1) temps(2) temps(3) temps(4)
100.0 100.2 100.4 100.6 100.8
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Variable subscripts
Dim temps(4) As Double
Dim m As Integer = 3
. . . . . .
What is temps( m + 1 ) ?
What is temps( m ) + 1 ?
temps(0) temps(1) temps(2) temps(3) temps(4)
100.0 100.2 100.4 100.6 100.8
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More about array index
Array index can be an integral expression of type Char, Short, Byte, or Integer.
It is programmer’s responsibility to make sure that an array index does not go out of bounds. The index must be within the range 0 through the array’s length minus 1.
Using an index value outside this range throws an IndexOutOfBoundsException. Prevent this error by using public instance method length.
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Aggregate Array Operations
numbers( 0)
numbers( 1) numbers( 2 )
numbers
values( 0)
values( 1) values( 2 )
values
Dim numbers( ) As Integer = {2, 4, 6}Dim values(3) As Integervalues(0) = 2values(1) = 4values(2) = 6
If (numbers = values) then…
2
4
6
2
4
6
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Aggregate Array Operations
numbers( 0)
numbers( 1) numbers( 2 )
numbers
values( 0)
values( 1) values( 2 )
values
numbers = values
If (numbers = values) then
…
2
4
6
2
4
6
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11.4 Examples of Declaring and Processing Arrays
Occupancy RatesConst BUILDING_SIZE as Integer = 350
Dim occupants(BUILDING_SIZE) AS Integer
Dim totalOccupants As Inteer
totalOccupants = 0
For counter = 0 To occupants.Length – 1
totalOccupants = totalOccupants +occupants(counter)
Next counter
occupants( 0)
occupants( 1) occupants( 2 )
.
.
.
. occupants( 349 )
occupants
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Sales Figures
Dim gourmetBurgers (5) As Double
gourmetBurgers( 0)
gourmetBurgers( 1) gourmetBurgers( 2 )
gourmetBurgers( 3 )
gourmetBurgers( 4 )
gourmetBurgers
246.41
271.04
350.13
640.69
177.42
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Using arrays for counters
Write a program to count the number of each alphabet letter in a text file.
letterASCII
‘A’ 65
‘B’ 66
‘C’ 67
‘D’ 68 . . . . . .
‘Z’ 90
This is my text file.
It contains many
things!
5 + 8 is not 14.
Is it?
datafile.dat
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Dim letterCount(25) As Integer
counts ‘A’ and ‘a’
counts ‘B’ and ‘b’
. . .
counts ‘ Y’ and ‘y’
counts ‘Z’ and ‘z’
letterCount ( 0 ) 2
letterCount ( 1 ) 0
. . . . . .
letterCount ( 24) 1
letterCount ( 25 ) 0
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Dim letter As Integer
While (dataFile.Peek<> -1)
letter = (Char(dataFile.Read ( ) )
If ((letter >= "A"c And letter <= "Z"c ) Or _
((letter >= "a"c And letter <= "z"c ) Then
index = (Int (Asc (letter.ToUpper(letter)) – Asc ("A"))
letterCount(index) = letterCount (index) + 1
End If
End While
Counting Frequency of Alphabetic Characters
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For index = 0 To letterCount.Length – 1
outFile.WriteLine ("The total number of " & _
Char(index + (Int (Asc ("A"))) & _
" " & letterCount (index))
Next
Printing Frequency of Alphabetic Characters
' print each alphabet letter and its frequency count
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Dim groceryItems (10) As String
( 0 ) “cat food”
( 1 ) “rice”
. .
. .
. .
( 8 ) “spinach”
( 9 ) “butter”
groceryItems
11.5 Array Of Objects (Strings)
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Dim groceryItems(10) As String
( 0 ) “cat food”
( 1 ) “rice” . .
. .
. .
( 8 ) “spinach”
( 9 ) “butter”
groceryItems Expression Class/Type
groceryItems Array
groceryItems(0) String
groceryItem(0).Chars(0) Char
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11.6 Passing Arrays as Arguments
In VB .NET an array is a reference type. What is passed to a method with an array parameter is the address of where the array object is stored.
The name of the array is actually a reference to an object that contains the array elements and the public instance variable Length.
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Public Function sumSales (ByRef data( ) As Integer) As Integer
Dim sum As Double = 0
Dim index As Integer
For index = 0 To data.Length – 1
sum = sum + data ( index )
Next index
Return sum
End Function
Passing an Array as Parameter
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Passing an Array as Parameter
Dim gourmetBurgers (5) As Double
outFile.WriteLine
(sumSales(gourmetBurgers))
gourmetBurgers( 0)
gourmetBurgers( 1) gourmetBurgers( 2 )
gourmetBurgers( 3 )
gourmetBurgers( 4 )
gourmetBurgers
246.41
271.04
350.13
640.69
177.42