A Introduction to Programming
Using Visual Basic 2010
（Eighth Edition）
David I. Schneider
Instructor
Name：Liang Jiankun
E-Mail：teacherljk@163.com
Phone: 23986531
Office: Computer Center
Chapter 6 – Arrays
6.1 Creating and Accessing Arrays
6.2 Using LINQ with Arrays
6.3 Arrays of Structures
6.4 Two-Dimensional Arrays
6.1 Creating and Accessing
Arrays
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•
•
•
•
•
•
Declaring an Array Variable
The Load Event Procedure
Implicit Array Sizing
Calculating an Array Value with a Loop
The ReDim Statement
Flag Variables
For Each Loops
6.1 Creating and Accessing
Arrays (continued)
•
•
•
•
•
Passing an Array to a Procedure
User-Defined Array-Valued Functions
Searching for an Element in an Array
Copying an Array
Split Method and Join Function
Simple Variable vs Array
• A variable (or simple variable) is a
name to which Visual Basic can assign
a single value
• An array variable is a collection of
simple variables of the same type with
same name to which Visual Basic can
efficiently assign a list of values.
Example advantage of array
Suppose you want to evaluate the exam grades
for 10 students and to display the scores which
are above the average
Dim Score1, Score2, Score3, Score4, Score5 As Integer
Dim Score6, Score7, Score8, Score9, Score10 As Integer
Dim Sum As Integer, Average As Double
Score1 = CInt(InputBox("Please input a new score"))
Score2 = CInt(InputBox("Please input a new score"))
Score3 = CInt(InputBox("Please input a new score"))
Score4 = CInt(InputBox("Please input a new score"))
Score5 = CInt(InputBox("Please input a new score"))
Score6 = CInt(InputBox("Please input a new score"))
Score7 = CInt(InputBox("Please input a new score"))
Score8 = CInt(InputBox("Please input a new score"))
Score9 = CInt(InputBox("Please input a new score"))
Score10 = CInt(InputBox("Please input a new score"))
Sum = Score1 + Score2 + Score3 + Score4 + Score5 + _
Score6 + Score7 + Score8 + Score9 + Score10
Example
Average = Sum / 10
txtAve.Text = CStr(Average)
If Score1 > Average Then
txtAbove.Text &= Score1 & "
End If
If Score2 > Average Then
txtAbove.Text &= Score2 & "
End If
If Score3 > Average Then
txtAbove.Text &= Score3 & "
End If
If Score4 > Average Then
txtAbove.Text &= Score4 & "
End If
If Score5 > Average Then
txtAbove.Text &= Score5 & "
End If
"
"
"
"
"
If Score6 > Average Then
txtAbove.Text &= Score6 & " "
End If
If Score7 > Average Then
txtAbove.Text &= Score7 & " "
End If
If Score8 > Average Then
txtAbove.Text &= Score8 & " "
End If
If Score9 > Average Then
txtAbove.Text &= Score9 & " "
End If
If Score10 > Average Then
txtAbove.Text &= Score10 & " "
End If
.
Example
Realize with Repetition-structure and simple variable
Dim Score As Integer
Dim Sum As Integer, Average As Double
For i = 1 To 10
Score = CInt(InputBox("Please input the " & i & " th score"))
Sum += Score
Next
The 10 scores must be input twice, because
a simple variable only store a single value.
Average = Sum / 10
txtAve.Text = CStr(Average)
For i = 1 To 10
Score = CInt(InputBox("Please input the " & i & " th score"))
If Score > Average Then
txtAbove.Text &= Score & " "
End If
Next
Example
No matter how many scores are there,
the program structure is the same.
Realize with array
Dim Score(9) As Integer
Dim Sum As Integer, Average As Double
For i = 0 To 9
Score(i) = CInt(InputBox("Please input the " & i & " th score "))
Sum += Score(i)
Next
Average = Sum / 10
txtAve.Text = CStr(Average)
For i = 0 To 9
If Score(i) > Average Then
txtAbove.Text &= Score(i) & " "
End If
Next
Array Terminology
Syntax：
Dim arrayName(n) As DataType
• 0 is the lower bound of the array
• n is the upper bound of the array–the last available
subscript in this array
• The number of elements, n + 1, is the size of the array.
Putting Values into an Array
score(0) = 10
subscript
Read: "score sub zero equals ten"
Which means that the number 10 is being stored at the first
location in the array called score because all arrays begin
counting at 0
In other words, score(0) is the first element of array score().
Example 1
Private Sub btnWho_Click(...) Handles btnWhoWon.Click
Dim teamNames(3) As String
Dim n As Integer
teamNames(0) = "Packers"
teamNames(1) = "Packers"
teamNames(2) = "Jets"
teamNames(3) = "Chiefs"
n = CInt(txtNumber.Text)
txtWinner.Text = teamName(n - 1)
End Sub
Super Bowl 美国橄榄球超级杯大赛
Load Event Procedure
Occurs as the Form loads in memory
Private Sub frmName_Load(...) Handles MyBase.Load
The keyword MyBase refers to the form being loaded. This
event procedure is a good place to assign values to an array.
Example 2: Form-Load procedure
The array can’t declared within any event procedure,
It must be Class-Scope.
Dim teamNames(3) As String
Private Sub frmBowl_Load(...) Handles MyBase.Load
teamNames(0) = "Packers"
teamNames(1) = "Packers"
teamNames(2) = "Jets"
teamNames(3) = "Chiefs"
End Sub
Private Sub btnWhoWon_Click(...) Handles btnWhoWon.Click
Dim n As Integer
n = CInt(txtNumber.Text)
txtWinner.Text = teamNames(n - 1)
End Sub
Initializing Arrays
Arrays may be initialized when created:
Dim arrayName() As DataType={value0,value1,value2,...,valueN}
declares an array having upper bound N and assigns value0 to
arrayName(0), value1 to arrayName(1), ..., and valueN to
arrayName(N).
Example:
Dim teamNames() As String={"Packers","Packers","Jets","Chiefs"}
Dim Score() As Integer={10, 20, 30, 40, 50, 60, 70, 80, 90, 100}
圆括号：parenthesis
大括号：curly bracket
逗号：comma
引号：quotation mark
Example 2: Simplified writing
You can’t specify the subscript here, the size
of the array is decided by the following list
Dim teamNames(3) As String
Private Sub frmBowl_Load(...) Handles MyBase.Load
Dim teamNames() As String={"Packers","Packers","Jets","Chiefs"}
End Sub
Private Sub btnWhoWon_Click(...) Handles btnWhoWon.Click
Dim n As Integer = CInt(txtNumber.Text)
txtWinner.Text = teamNames(n - 1)
End Sub
Text Files
Some times text file is used to offer the initial values of
array. Such as Presidents.txt, States.txt etc.
• Can be created, viewed, and managed by word processors
or by the Visual Basic IDE
• Have the extension txt
• Normally placed in the bin\Debug folder in the Solution
Explorer.
Using a Text File to Populate
a String Array
• Assume the text file named
theNamesOfTheFirstSixPresidents.txt
lies in the bin\Debug folder.
• The text file can be used to fill string array with
the statement
Dim PNames() As String
=IO.File.ReadAllLines("theNamesOfTheFirstSixPresidents.txt")
• The array PNames will have size 6 and upper
bound 5.
Array Methods
Dim PNames() As String
=IO.File.ReadAllLines("theNamesOfTheFirstSixPresidents.txt")
Method Name
Value
Value in this case
arrayName.Count
number of elements
arrayName.Max
highest value(不区分大小写数字比字母小)
Thomas Jefferson
arrayName.Min
lowest value(不区分大小写数字比字母小)
George Washington
arrayName.First
first element
George Washington
arrayName.Last
last element
John Q. Adams
arrayName.Average Average value(需为数值型数组)
arrayName.Sum
The sum of the elements(需为数值型数组)
6
Array Methods (continued)
• The upper bound of arrayName is
arrayName.Count – 1
• arrayName.First is the same as
arrayName(0)
Populating a Numeric Array
with a Text File
If you want to evaluate the elements value
numerically (such as average, sum etc.),
you should change the array from string
to numeric type.
Dim FinalScores() As String=IO.File.ReadAllLines("Scores.txt")
Dim Scores(FinalScores.Count-1) As Integer
For i As Integer = 0 To FinalScores.Count-1
Scores(i) = CInt(FinalScores(i))
lstOutput.Items.Add(Scores(i))
Next
lstOutput.Items.Add("The highest value is " & Scores.Max)
lstOutput.Items.Add("The lowest value is " & Scores.Min)
lstOutput.Items.Add("The average is " & Scores.Average)
lstOutput.Items.Add("The sum is " & Scores.Sum)
Using Loops Instead of Methods
Dim ages() As Integer = {55, 56, 61, 52, 69, 64, 46, 54, 47}
Dim max As Integer = ages(0)
For i = 1 To ages.Count - 1
If ages(i) > max Then
max = ages(i)
End If
Next
txtOutput.Text = "Greatest age: " & max
Output: Greatest age: 69
Using Loops Instead of Methods Cont.
Another way, you may find the max element with the subscript
Dim ages() As Integer = {55, 56, 61, 52, 69, 64, 46, 54, 47}
Dim max As Integer = 0
For i = 1 To ages.Count - 1
If ages(i) > ages(max) Then
max = i
End If
Next
txtOutpxt = "Greatest age: " & ages(max) & ". It’s the " & max+1 & "th
element"
Output: Greatest age: 69. It’s the 5th element
ReDim Statement
You can’t change the type of an existing array,
so there is no As DataType
• The size of an array may be changed after it
has been created with the following statement
ReDim arrayName(m)
• arrayName is the name of the already declared array
• m is an Integer literal, variable, or expression
• the upper bound of the array is changed to m.
Preserve Keyword
ReDim arrayName(m)
• resets all values to their default.This can be
prevented with the keyword Preserve
ReDim Preserve arrayName(m)
• resizes the array and retains as many values
as possible.
Flag Variables
Flag variables have type Boolean. They are used when looping
through an array. It may provide information to be used after loop
terminates. Or, allows for the early termination of the loop.
Dim Score() As String
Private Sub Button1_Click(…) Handles Button1.Click
Score = IO.File.ReadAllLines("scores.txt")
For i = 0 To Score.Count - 1
lstoutput.Items.Add(Score(i)) Dim n As String = TextBox1.Text
Dim Found As Boolean = False
Next
For i = 0 To Score.Count - 1
End Sub
If Score(i) = n Then
Found = True
Exit For
End If
Next
If Found = True Then
MessageBox.Show(n & " is found.")
Else
MessageBox.Show("There is no " & n & " in the array.")
End If
For Each Loops
For i As Integer = 0 To ages.Count - 1
If ages(i) > max Then
max = ages(i)
End If
Next
The Looping variable can be any name
can be replaced with
For Each x As Integer In ages
If x > max Then
max = x
End If
Next
For i = 0 To Score.Count - 1
If Score(i) = n Then
Found = True
Exit For
End If
Next
can be replaced with
For each Mark as string In Score
If mark = n Then
Found = True
Exit For
End If
Next
Passing an Array Element
A single element of an array can be passed
to a procedure just like any ordinary numeric or
string variable.
Private Sub btnDisplay_Click(...) Handles btnDisplay.Click
Dim num(20) As Integer
num(5) = 10
lstOutput.Items.Add(Triple(num(5)))
End Sub
Function Triple(ByVal x As Integer) As Integer
Return 3 * x
End Function
The header of the Function procedure uses
the name with an empty set of parentheses
Passing Arrays to Procedures cont.
Function Range(ByVal x() As Integer) As Integer
Dim Large, Small, N As Integer
Large = x.Max
Small = x.Min
N = Large - Small
Return N
End Function
The calling statement uses the name
of the array without parentheses.
Private Sub btnCalculate_Click(...) Handles btnCalculate.Click
Dim ages() As Integer = {55, 56, 61, 52, 69, 64, 46, 54, 47}
txtOutput.Text = “The range of the array is " & Range(ages)
End Sub
User-Defined Array-Valued Functions
Headers have the form
Function FunctionName(ByVal var1 As Type1, ByVal var2 As Type2, ...)
As DataType()
Function Prime(ByVal x() As Integer) As Boolean()
Dim JG(x.Count - 1) As Boolean ‘记录结果
For i = 0 To x.Count - 1
Dim flag As Boolean = True
For j = 2 To x(i) – 1
此函数的返回值为一个布
If x(i) Mod j = 0 Then
尔型的数组，每个元素的
flag = False
Exit For
值就是数组x()对应元素的
End If
素数判断结果
Next j
If flag Then
JG(i) = True
Else
JG(i) = False
End If
Next i
Return JG
End Function
Searching for an Element in an Array
numVar = Array.IndexOf(arrayName, value)
• assigns to numVar the index of the first occurrence of value in arrayName.
• Or assigns -1 if the value is not found.
Dim colors() As String = IO.File.ReadAllLines("Colors.txt")
Private Sub btnDetermine_Click(…) Handles btnDetermine.Click
Dim color As String = txtColor.Text
If Existing(color, colors) Then
txtOutcome.Text = color & " is a crayola color."
Else
txtOutcome.Text = color & " is not a crayola color."
End If
End Sub
Function Existing(ByVal x As String, ByVal y() As String) As Boolean
If Array.IndexOf(y, x) = -1 Then
Return False
Else
Return True
End If
End Function
Copying an Array
arrayOne = arrayTwo
makes arrayOne an exact duplicate of
arrayTwo
If only arrayOne and arrayTwo have been
declared with the same data type, no matter
what is the size of arrayOne .
They share the same location in memory.
Copying an Array Cont.
Dim a() As Integer = {10, 20, 30, 40, 50}
Dim b() As Integer
b = a Dim a() As Integer = {10, 20, 30, 40, 50}
As Integer
For i =Dim
0 Tob(4)
4
b = a Dim a() As Integer = {10, 20, 30, 40, 50}
ListBox1.Items.Add(b(i))
Dim
b(2)
As Integer
For
i
=
0
To
4
Next
b = a Dim a() As Integer = {10, 20, 30, 40, 50}
ListBox1.Items.Add(b(i))
Dim
b(8)
As Integer
ListBox1.Items.Add("Ubound(b)="
& b.Count - 1)
For
i
=
0
To
4
Next
b=a
ListBox1.Items.Add(b(i))
ListBox1.Items.Add("Ubound(b)="
& b.Count - 1)
For
i
=
0
To
4
Next
ListBox1.Items.Add(b(i)) & b.Count - 1)
ListBox1.Items.Add("Ubound(b)="
Next
ListBox1.Items.Add("Ubound(b)=" & b.Count - 1)
.
结论：只要数组a和b都是一维数组且类型相同，
无论数组b原来的下标如何，都会被重新定义为和a一样！
Copying an Array Cont.
Dim a() As Integer = {10, 20, 30, 40, 50}
Dim b() As Integer
Dim a() As Integer = {10, 20, 30, 40, 50}
b=a
Dim b(4) As Integer
For i = 0 To 4
For i = 0 To 4
b(i) = b(i) / 2
b(i) = a(i)
Next
Next
For i = 0 To 4
For i = 0 To 4
b(i) = b(i) / 2
ListBox1.Items.Add(a(i))
Next
Next
For i = 0 To 4
结论：数组a和b经过直接复制操
ListBox1.Items.Add(a(i))
作后，它们在内存中指向同一位
Next
置（同一个数组的两个不同名称）
结论：数组a和b经过逐元素赋值后，它们
只有初始值相同，其它无任何联系。
Split Method
• Facilitates working with text files.
• Split can convert a string containing commaseparated data into a string array.
• The 0th element of the array contains the text
preceding the first comma, the 1st element
contains the text between the first and
second commas, ..., and the last element
contains the text following the last comma.
Split Example
For instance, suppose the string array employees
has been declared without an upper bound, and the
string variable line has the value “Bob,23.50,45”.
Dim employees() as String
employees = line.Split(","c)
•sets the size of employees to 3
•sets employees(0) = “Bob”
•sets employees(1) = “23.50”
•sets employees(2) = “45”
Split Comments
employees = line.Split(","c)
• In this example, the character comma is called the
delimiter for the Split method, and the letter c specifies
that the comma has data type Character instead of String
• Any character can be used as a delimiter. If no character
is specified, the space character will be used as the
delimiter by default.
Example
Private Sub btnConvert_Click(...) Handles btnConvert.Click
Dim stateData(), line As String
line = "California,1850,Sacramento,Eureka"
stateData = line.Split(","c)
For Each entry As String In stateData
lstOutput.Items.Add(entry)
Next
End Sub
California
1850
Sacramento
Eureka
Join Function
The reverse of the Split method is the Join function.
Join concatenates the elements of a string array into a
string containing the elements separated by a specified
delimiter.
Dim numbers() As String = {"One", "Two", "Three", "Four"}
Dim s As String
s = Join(numbers, "-")
txtOutput.Text = s
Output: One-Two-Three-Four
Out of Range Error
The following code references an array element
that doesn't exist. This will cause an error.
Comments and Exercises
Comments6.1 P206
Exercises6.1 P207
6.2 Using LINQ with Arrays
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•
•
•
•
•
•
•
LINQ Queries
The Distinct Operator
The ToArray Method
Use of Function Procedures in Queries
The Let Operator
The OrderBy Operator
The DataSource Property
Binary Search
What is LINQ?
• LINQ stands for Language INtegrated Query
• A query is a request for information
Note: Option Infer must be set to ON in order to use LINQ
LINQ Query
Code of the form
range variable
Dim queryName = From var In arrayName source data
Where [condition on var] filter data过滤数据
Select var Project data投影数据
query operators
• declares the variable queryName and assigns to it a sequence of the
values from arrayName that satisfy the stated condition
• The values in the sequence can be converted to an array, displayed in a
list box, or written to a text file
Example 1
'States.txt contains names of the 50 states
Dim states() As String = IO.File.ReadAllLines("States.txt")
Dim stateQuery = From s In states
Where s.Length = 5
Select s
For Each s As String In stateQuery
lstStates.Items.Add(s)
Next
lstStates.Items.Add(stateQuery.Count)
lstStates.Items.Add(stateQuery.Min)
lstStates.Items.Add(stateQuery(1))
Maine缅因州, Texas德克萨斯州, Idaho爱达荷州
Example 2
Dim nums() As Integer = {7, 11, 12, 14, 15, 16, 18, 21, 30}
Dim numQuery = From n In nums
Where n > 10 And n < 20 And n Mod 2 = 0
Select n
For Each m As Integer In numQuery
lstBox.Items.Add(m)
Next
lstBox.Items.Add("")
lstBox.Items.Add("Largest number: " & numQuery.Max)
lstBox.Items.Add("Second number: " & numQuery(1))
lstBox.Items.Add("Sum of numbers: " & numQuery.Sum)
Another Variation of Example 2
Dim S() As Integer = {5, 12, 8, 7, 11, 5, 8}
Dim numQuery = From num In S
Where num < 10
Select num * num
changed
For Each X As Integer In numQuery
lstBox.Items.Add(X)
Next
Output: 25, 64, 49, 25, 64
Distinct Operator
The sequence created with a LINQ query might contain
duplicate elements. Duplicates can be eliminated with key
word Distinct.
Dim S() As Integer = {5, 8, 7, 5, 8}
Dim numQuery = From num In S
Select num
Distinct
There is no Where clause. It means select all the elements
For Each X As Integer In numQuery
lstBox.Items.Add(X)
Next
Output: 5, 8, 7
ToArray Method
Also the sequence returned by a LINQ query has many of the features of
an array(it has Max, Min, Sum, Average, Count, First, Last methods and
subscripts just like an array), but the query is not an array variable because it
hasn’t datatype and its values can’t be altered with assignment statements.
The ToArray method can convert it to an array variable
Dim nums() As Integer = {8, 12, 5, 7, 12, 5}
Dim numQuery = From n In nums
Where n < 10
Select n
Distinct
Dim Small() As Integer = numQuery.ToArray
lstBox.Items.Clear()
For i = 0 To Small.Count - 1
lstBox.Items.Add(Small(i))
Next
RESULT：8, 5, 7.
Function Procedures in Queries
Function procedures may be used in Where and Select clauses
Dim nums() As Integer = {5, 7, 8, 11, 12}
Dim numQuery = From n In nums
Where IsPrime(n) = True
Select Triple(n)
For Each m As Integer In numQuery
lstBox.Items.Add(m)
Next
Let Operator
A Let operator gives a name to an expression and makes
queries easier to read
Function LargestDivisor(ByVal x As Integer) As Integer
Dim Max As Integer = 2
For i = 3 To x \ 2
If x Mod i = 0 Then
Max = i
End If
Next
Dim nums() As Integer = {15, 7, 39, 11, 21}
Return Max
Dim numQuery = From n In nums
End Function
Where IsPrime(n) = False
返回合数的最大质因子
Let ZuiDaYinZi = LargestDivisor(n)
(不含1和自身)
Select ZuiDaYinZi
For Each m As Integer In numQuery
lstBox.Items.Add(m)
Next
Order By Operator
Order By Operator may sort string values into alphabetical
order or sort numbers into numeric order either ascending or
descending(Ascending by default)
Dim nums() As Integer = {15, 17, 39, 5, 21, 13}
Dim numQuery = From n In nums
Where IsPrime(n) = True
Order By n Descending
Select n
For Each m As Integer In numQuery
lstBox.Items.Add(m)
Next
Example 5..
Dim stateQuery = From state In IO.File.ReadAllLines("States.txt")
Order By state.Length, state Descending
Select state
For Each state As String In stateQuery
lstOutput.Items.Add(state)
Next
如果想只显示长度大于5的州名称，如何改写？
如果不需要过滤也不需要其它处理，只是为了对数
组进行排序，大可不必动用LINQ来进行Order By，
Array.Sort(数据名)就可以实现对数组的简单升序排
序 。再进行一次Array.Reverse(数组名)就是降序。
DataSource Property
The DataSource property fills a list box with the values returned
by a query lstBox.DataSource = queryName.ToList
The first entry will be highlighed by default. The highlighting
can be eliminated with lstBox.SelectedItem = Nothing
Dim stateQuery = From state In IO.File.ReadAllLines("States.txt")
Order By state.Length, state Descending
Select state
lstOutput.DataSource = stateQuery.ToList
'lstOutput.SelectedItem = Nothing
Binary Search
A large array in ascending order is most efficiently searched
with a binary search. The Binary Search method looks for a
value in the array by first determining in which half of the array it
lies. The other half is then ignored, and the search is narrowed
to the retained half.
A statement of the form
numVar = Array.BinarySearch(arrayName, value)
Assigns to numVar the index of an occurrence of the
requested value in arrayName. If the value is not found, then a
negative number is assigned to numVar.
注意：要想使用二分法查找，这个数组必须是升序的！
Comments and Exercises
Comments6.2 P217
Exercises6.2 P218
6.3 Arrays of Structures
•
•
•
•
•
•
•
Structures
Arrays of Structures
The DataGridView Control
Searching an Array of Structures
Using General Procedures with Structures
Displaying and Comparing Structure Values
Complex Structures (optional)
Structures
A structure is a group of different types of data, Also
called a UDT (User Defined Type)
Sample structure definition:
Structure Nation
Dim Name As String
Dim Continent As String
Dim Population As Double 'in millions
Dim Area As Double
'in square miles
End Structure
Structure Definition
Each subvariable in a structure is called a member
To declare a variable of a structure type:
Dim Country As Nation
Each member is accessed via
variableName.memberName
For example:
Country.Name = "China"
Country.continent = "Asia"
Example 1
Dim Country As Nation
Country.Name = "China"
Country.Continent = "Asia"
Dim Country =As
Nation
Country.Population
"1332.5"
Dim line
As String = "China,Asia,1332.5,3696100"
Country.Area
= "3696100"
Dim data() As String = line.Split(","c)
Country.Name = data(0)
Country.Continent = data(1)
Country.Population = CDbl(data(2))
Country.Area = CDbl(data(3))
Example 1 (continued)
'Display data in text boxes
txtName.Text = country.name
txtContinent.Text = country.continent
txtPop.Text = FormatNumber(1000000*country.population,0)
txtArea.Text = FormatNumber(country.area, 0) & " square miles"
txtDensity.Text = FormatNumber(1000000*country.population /
country.area) & " people per square mile"
Text File: UN.txt
The file UN.txt contains 192 countries each per line
There are 4 fields (name, continent, pop in millions,
area in square miles) for each country
For Example:
Canada,North America,32.9,3855000
France,Europe,63.5,211209
New Zealand,Australia/Oceania,4.18,103738
Australia,Australia/Oceania,21.9,2967909
China,Asia,1332.5,3696100
United States,North America,307.2,3794066
Example 3
Structure Nation
Dim Name As String
Dim Continent As String
Dim Population As Double
Dim Area As Double
End Structure
Dim nations(191) As Nation 'declare array
Dim line, data() As String
'fill with UN.txt
Dim countries() As String = IO.File.ReadAllLines("UN.txt")
For i As Integer = 0 To 191
line = countries(i) 'Such as"China,Asia,1332.5,3696100"
data = line.Split(","c)
nations(i).name = data(0)
nations(i).continent = data(1)
nations(i).population = CDbl(data(2))
nations(i).area = CDbl(data(3))
Next
Example 3: More Partial Code
Dim selectedContinent As String = lstContinents.Text
Dim query = From country In nations
Where country.continent = selectedContinent
Order By country.area Descending
Select country.name
For Each nation In query '此时query的结果都是国家的名称
lstCountries.Items.Add(nation)
Next
Structure College
Structure College
Dim name As String
Dim state As String 'state abbreviation
Dim yearFounded As Integer
End Structure
The file Colleges.txt contains the colleges founded before 1800 in US.
There are 3 fields (name, state, year founded) in each line
For Example:
Harvard U.,MA,1636
Columbia U.,NY,1754
哈佛,马萨诸塞州(Massachusetts)
哥伦比亚大学,纽约州(New York)
Example 4: Earliest Colleges
Dim colleges() As College
Private Sub frmColleges_Load(…) Handles MyBase.Load
Dim schools() = IO.File.ReadAllLines("Colleges.txt")
ReDim colleges(schools.Count - 1)
Dim line As String
Dim data() As String 'hold data for a single college
For i As Integer = 0 To schools.Count - 1
line = schools(i) 'such as "Columbia U.,NY,1754"
data = line.Split(","c)
colleges(i).name = data(0)
colleges(i).state = data(1)
Structure College
Dim name As String
colleges(i).yearFounded = CInt(data(2))
Dim state As String
Next
Dim yearFounded As Integer
End Sub
End Structure
Example 4: Earliest Colleges
Cont.
Private Sub btnDisplay_Click(….) Handles btnDisplay.Click
Dim query = From C In colleges
Where C.state = mtbState.Text.ToUpper
Order By C.name Ascending
Select C.name, C.yearFounded '提取出了其中的两列
lstColleges.Items.Clear()
For Each institution In query
lstColleges.Items.Add(institution.name & " " & institution.yearFounded)
Next
End Sub
How to show information with
several columns
• Method 1: Output with ListBox normally
• Method 2: Formatting output with zones
• Method 3: With DataGridView control
Formatting Output with Zones
Method 2:
• Use a fixed-width font such as Courier New
• Divide the characters into zones with a format string
Dim fmtStr As String = "{0, 15}{1, 10}{2, 8}"
lstOutput.Items.Add(String.Format(fmtStr, data0, data1, data2))
Formatting Output with Zones (Display in tabular form)
DataGridView Control
Method 3:
•
•
•
•
Useful when two or more pieces of information are to be displayed
Lies in the Data group or All Windows Forms group of the Toolbox
Displays a table with column headers
AutoSizeColumnsMode property is used to set the width of column.
DataSource Method
When the Select clause of a query contains two or
more items, the pair of statements
DataGridView1.DataSource = queryName.ToList
DataGridView1.CurrentCell = Nothing
displays the items of data in a DataGridView control.
(The second statement, which is optional, keeps all
cells unhighlighted.)
DataGridView Headers
• By default the rows have blank headers and the
column headers contain the names of the items in
the Select clause
column
headers
row
headers
DataGridView Headers (cont.)
• Row headers can be removed by setting the RowHeadersVisible
property of the DataGridView control to False.
• A column header can be customized with a statement such as
DataGridView1.Columns("Name").HeaderText = "University"
DataGridView1.Columns("YearlyTuition").HeaderText = "Tuition"
DataGridView1.Columns("YearFounded").HeaderText = "Year Founded"
Searching an Array of Structures
The Where clause of a query can be used to locate
specific items(定位出那些具有某个特定值的项，例如某个州、某个成立年份等). If
the query returns a sequence, a method such as First,
Last, Max, Min and so on may be used to display a
certain item. Example:
Dim query = From institution In University
Where institution.State = txtState.Text
Order By institution.YearFounded Ascending
Select institution
txtName.Text = query.First.Name
txtYear.Text = CStr(query.First.YearFounded)
Comments and Exercises
Comments6.3 P233
Exercises6.3 P234
6.4 Two-Dimensional Arrays
•
•
•
•
Declaring a Two-Dimensional Array Variable
Implicit Array Sizing and Initialization
The ReDim Statement
Filling a Two-Dimensional Array with a Text File
Declaring a Two-Dimensional
Array Variable
• One-dimensional arrays store a list of items of the
same type
• Two-dimensional arrays store a table of items of the
same type.
• Consider the rows of the table as numbered 0, 1,
2,…, m and the columns numbered 0, 1, 2, …, n.
Then the array is declared with
Sized (指定大小的) two-dimensional array
Dim arrayName(m, n) As DataType
• The item in ith row, jth column write as arrayName(i,j)
Implicit Array Sizing and
Initialization
A two dimensional array can be initialized when it is
Unsized (未指明大小的) two-dimensional array
declared as
Dim arrayName(,) As DataType={{row0},{row1},...,{rowN}}
• It declares a two-dimensional array where row0
consists of the entries in the top row of the
corresponding table delimited by commas.
For Example:
Dim marks(,) As Integer={{50,20,80},{40,90,70},{60,10,30}}
50
20
80
40
90
70
60
10
30
Road-Mileage Array
Chicago
LA
NY
Philly
Chicago
0
2054
802
738
LA
2054
0
2786
2706
NY
802
2786
0
100
Philly
738
2706
100
0
Dim rm(,) As Double = {{0,2054,802,738},{2054,0,2786,2706},
{802,2786,0,100},{738,2706,100,0}}
declares and initializes an array of road-mileages table
Some elements of the array are
rm(0,0)=0, rm(0,1)=2054, rm(1,2)=2786
GetUpperBound Method
After execution of the statement
Dim arrayName(m, n) As varType
the value of arrayName.GetUpperBound(0) is m, and
the value of arrayName.GetUpperBound(1) is n.
第几维的上界，下界恒为0
Dim seat(20, 15) As Integer
seat.GetUpperBound(0) is 20
seat.GetUpperBound(1) is 15
ReDim a Two-Dimensional Array
An already-created array can be resized with
ReDim arrayName(m, n)
no matter it is a sized or unsized array
But it will loses the current contents, or with
ReDim Preserve arrayName(m, n)
• When Preserve is used, only the columns (the right
most dimension) can be resized
• ReDim cannot change the number of dimensions in
the array.
如果定义这个多维数组时，根本就不知道每一维的大小。
可以这样定义二维数组 Dim a(,) As DataType
可以这样定义三维数组 Dim a(,,) As DataType
……
Filling a Two-Dimensional
Array with a Text File
Dim rm(3, 3) As Double 'road mileage
Dim rowOfNums() As String =IO.File.ReadAllLines("Distances.txt")
Dim line, data() As String
For i As Integer = 0 To 3
line = rowOfNums(i)
'The string consists 4 numbers
data = line.Split(","c)
'The 4 distances
For j As Integer = 0 To 3
rm(i, j) = CDbl(data(j))
Next
Next
Private Sub btnShow_Click(…) Handles btnShow.Click
Dim Row, Col As Integer
Row = CInt(txtOrig.Text)
Col = CInt(txtDest.Text)
If (Row >= 1 And Row <= 4) And (Col >= 1 And Col <= 4) Then
txtMiles.Text = CStr(rm(Row - 1, Col - 1))
Else
MessageBox.Show(“the numbers must between 1 and 4", "Error")
End If
End Sub
Comments and Exercises
Comments6.4 P245
Exercises6.4 P245