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Lecture Summary for IT 236 on 6/29/05

Review Questions

1. Show the variable trace and predict the output. Test your answer using VB.NET.
   Public Sub Main()
       Dim x, y As Integer
       Dim s, t As String

       x = 0
       y = 1
       s = "abcdefghijklmnopqrstuvwxyz"
       t = ""
       While x <= 25
          t = t & s.Substring(x, y)
          x = 2 * x + 1
       End While
       s = t.Insert(3, "***")
       WriteLine(s & x & y)
   End Sub

   Ans: Trace table:
   

   x	y	s	t
   0	1	"abcdefghijklmnopqrstuvwxyz"	""
   1	1	"abcdefghijklmnopqrstuvwxyz"	"a"
   3	1	"abcdefghijklmnopqrstuvwxyz"	"ab"
   7	1	"abcdefghijklmnopqrstuvwxyz"	"abdh"
   15	1	"abcdefghijklmnopqrstuvwxyz"	"abdhp"
   31	1	"ab***dhp"	"abdhp"

   Output:
   ab***dhp311

2. Show the variable trace and predict the output. Test your answer using VB.NET.
   Public Sub Main( )
       Dim a( ) As Integer = {6, 2, 3}
       Dim t As Integer

       If a(0) > a(1) Then
          t = a(1)
          a(1) = a(0)
          a(0) = t
       End If

       If a(1) > a(2) Then
          t = a(2)
          a(2) = a(1)
          a(1) = t
       End If

       If a(0) > a(1) Then
          t = a(1)
          a(1) = a(0)
          a(0) = t
       End If

       For Each t In a
          WriteLine(t)
       Next
   End Sub

   Ans: Trace table:
   

   a(0)	a(1)	a(2)	t
   6	2	3
   2	6	3	2
   2	3	6	3

   Output:
   2
   3
   6

3. Write a console application that counts how many blanks there are in an input string s.

   Ans: See the CountBlanks example.

4. Write a console application that reads strings from an input file and writes them out reversed to an output file.

   Ans: See the Reverse1 example.

5. Write a user defined function that inputs a string and returns the reversed string. Write a Main method to test your function.

   Ans: See the Reverse2 example.

6. Write user defined functions according to the following specifications. Test each function in the Console Application Main method.
   1. Write a function named vowelCount that returns the number of vowels in a string.

      Ans: See the VowelCount.

   2. Write a function named IsFourLetter word. It should return True if the length of the input string is four. It should return and False otherwise.

      Ans: See the IsFourLetterWord.

7. Write a For loop that adds the strings "A", "B", "C", ... , "Z", one per line, to a multiline text box.
   Hint: the ascii codes of these letters are 65 to 90. Use the Chr function that changes an ascii code into a character.

Introduction to Relational Databases

• A relational database consists of one or more is a rectangular tables of data.

• Here is the table PersonData. Each column is a property or attribute of the data. Each row represents a person. A row is also called a tuple

  Name	Gender	Age
  Mary	F	23
  Robert	M	31
  Sally	F	35
  Jane	F	28
  Tony	M	30
  Alice	F	41
  Scott	M	27
  Larry	M	49

• The traditional language to use for manipulating relational databases is SQL (Structured Query Language).

• The SELECT statement is used for extracting data from a table.

• Some SQL statements for modifying tables are DELETE, INSERT, and UPDATE.

• Use a FROM clause to select columns from a table:
  SELECT Name, Age FROM PersonData

• Use * to select all the columns from a table:
  SELECT * FROM PersonData

• Use a WHERE clause to select rows from a table:
  SELECT * FROM PersonData WHERE Gender = 'F'
  SELECT Name FROM PersonData WHERE Age = 23
  SELECT * FROM PersonData WHERE Name = 'Jane'
  SELECT Name, Gender FROM PersonData
      WHERE Age <= 20 AND 30 < Age

• Note that single quotes are used in SQL to denote text constants.

• See the SQLExamples example.

Some ADO.NET Objects for Database Processing

• OleDbConnection   Manages the connection between the Access database (.mdb) file and the .NET application.

• OleDbInsertCommand   Manages an SQL INSERT command for modifying a table via a DataAdapter object.

• OleDbSelectCommand   Manages an SQL SELECT command for filling a DataSet object with data from a table via a DataAdapter object.

• Three other families of database objects exist, in addition to the OleDb objects:
  
• OleDbDataAdapter   Facilitates the two-way data flow between between the Access database file and DataSet objects.

• DataSet   Contains the in memory data from a table for use by a VB.NET application.

• Data Bound Control   A control can be bound to a dataset so that data is automatically transfered from the dataset to a property of the control.

• Other families of ADO.NET Objects are Odbc, Oracle, and Sql:
  OdbcCommand, OdbcConnection, OdbcDataAdapter,
  OracleCommand, OracleConnection, OracleDataAdapter,
  SqlCommand, SqlConnection, SqlDataAdapter.

Using ADO.NET OleDb Data Objects

• Uses Connection, DataAdapter, and Dataset objects without writing code.

• Important: If you use method 1 for the FlightInfo2 Project, you must put the database in c:\Database, resulting in the path
  c:\Database\flights.mdb.

• Here are the directions for Method 1.

• Following these directions produces the Groceries1 example.

• Use the DataAdapter method Fill to move data from the DataAdapter object to the DataSet object.

• Use the DataAdapter method Update to move data from the DataSet object to the DataAdapter object.

• Creates the Connection, DataAdapter, and Dataset objects dynamically with code.

• The document Code for Common Database Operations explains how to write the code for Methods 2 and 3.

• See the Groceries2 example.

• Creates database objects at runtime using code. Accesses the DataSet object using the built in collections in that object; do not use data bindings.
• The document Code for Common Database Operations explains how to write the code for Methods 2 and 3.

• A Dataset object contains an array called Tables.

• Each array item of Tables contains objects of type DataTable contains Columns and Rows.

• Each array item of Columns has the ColumnName property.

• Each array item of Rows contains an ItemArray collection.

• The items in ItemArray can be accessed by index or column name.

• Example: To assign to x the item of table 0, row 3, and column 4:
  x = ds.Tables(0).Rows(3).ArrayItem(4)

• See the Groceries3 example.

• These examples show how to write dynamic SQL statements depending on the control values:
  Groceries4   Groceries5

Practice Problem

1. Redo the PhoneNumbers Example using the database PhoneNumbers.mdb in PhoneNumbers.zip.

Two New Controls

• See the ListBox, ComboBox examples, and Groceries6

The FlightInfo2 Project

• Discuss the FlightInfo2 Project.

The Random Object

• A Random object generates pseudorandom numbers.

• Use the Next method of the Random class to obtain random integers.

• Example:
  Dim r As New Random
  number = r.Next(min, max)
  generates a random number between min and max inclusive.

• Use the NextDouble method to generate random doubles between 0.0 and 1.0.

• See the RandomNumbers example.

• See the ConsultantBSGenerator examples.

Practice Problems

1. Write a Console application that simulates 60,000 rolls of a die. Count how many sixes are obtained.

   Ans: See the DieRolls (W) example.

2. Write a Console application that rolls a pair of dice repeatedly. Count how many rolls are needed to roll snake eyes (a pair of ones).

   Ans: See the SnakeEyes (W) example.

Drawing in a PictureBox Control

• Create a Paint event handler for the picture box with this header:
  Private Sub picDisplay_Paint(ByVal sender As Object, _
      ByVal e As System.Windows.Forms.PaintEventArgs) _
      Handles picDisplay.Paint

  End Sub

• Create a Pen object:
  Dim p As New Pen(Color.Black)

• Create a Brush object:
  Dim b As New SolidBrush(Color.Red)

• Create a Font object:
  Dim b As New Font("arial", 14, FontStyle.Bold)

• Call one of the Graphics drawing methods:
  e.Graphics.DrawRectangle(p, x, y, w, h)
  e.Graphics.FillRectangle(b, x, y, w, h)
  e.Graphics.DrawEllipse(p, x, y, w, h)
  e.Graphics.FillEllipse(b, x, y, w, h)
  e.Graphics.DrawString("Message", f, b, x, y)

• Here is an example of drawing in a picture box:
  Drawing   (W).

• The Paint event occurs in these five situations:
  1. The form is loaded and displayed.

  2. The form in restored after being minimized.

  3. The form is exposed after being hidden by another form.

  4. The form is resized exposing a region that was previously hidden.

  5. The Invalidate method of the form or control called.

Capturing Mouse Data

• The MouseDown, MouseUp, and MouseMove event handlers of the PictureBox object pass back the e object, which has X and Y properties. The X and Y properties indicate the location of the mouse event.

• See the MouseData Example.

• The Invalidate method of the form causes the Paint event of the picture box to fire.

Creating Controls Dynamically

• Here is an example of how to create a Button control at run time using code. Put this code in the form load event handler.

  b = New Button
  b.Location = New Point(50, 50)
  b.Size = New Size(60, 100)
  b.Text = "Push Me"
  Me.Controls.Add(b)
  b.Show()