Computer Programming Concepts and Visual Basic David I. Schneider

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324 Computer Programming Concepts and Visual Basic TABLE 11.2 Countries Country pop1995 currency Brazil 155.8 real China 1185.2 yuan India 846.3 rupee Indonesia 195.3 rupiah Japan 125.0 yen Mexico 85.6 peso Nigeria 95.4 naira Russia 148.2 ruble USA 263.4 dollar Source: An Urbanized World—Global Report on Human Settlements 1996, a report presented at Habitat II, a UN conference on the world’s cities held in Istanbul in June 1996. A database (or relational database) is a collection of one or more (usually related) tables that has been created with database management software. The best known dedicated database management products are Access, Btrieve, dBase, FoxPro, and Paradox. Every version of Visual Basic 6.0 can manage, revise, and analyze a database that has been created with one of these products. Section 11.3 shows how to create a database with Visual Data Manager, a miniversion of Access that is supplied with Visual Basic. Section 11.3 also gives a code template for creating a database programmatically. The databases used in this chapter can be found in the collection of files accompanying this text. The database files have the extension .MDB. For instance, the file MEGAC- TY1.MDB is a database file containing the two tables presented on the preceding page. (Note: MDB files should be copied from the CD onto a hard drive and accessed from the hard drive.) THE DATA CONTROL Visual Basic communicates with databases through the data control. Data controls can read, modify, delete, and add records to databases. The following walkthrough uses a data control to connect Visual Basic to the database MEGACTY1.MDB. ■ A DATA CONTROL WALKTHROUGH 1. Press Alt/File/New Project and double-click on Standard EXE. 2. Double-click on the data control icon. Set its Name property to datCities and its Caption property to Cities. 3. Stretch it horizontally to see the caption Cities. 4. Select the DatabaseName property and set it to the filespec for the file MEGACTY1.MDB. An Open File dialog box will help you locate the file. 5. Select the RecordSource property and click on the down-arrow button at the right of the Settings window. The names of the two tables in the database, Cities and Countries, are displayed. 6. Select Cities. 7. Place a text box, txtCity, on the form. Text boxes are said to be data-aware because they can be bound to a data control and access its data. 8. In the Properties window, select the DataSource property of txtCity.
9. Click on the down arrow to the right of the Settings box and select datCities. 10. Select the DataField property and click on the down arrow at the right of the Settings box. You will see the names of the different fields in the table. 11. Select the field city. The text box now is said to be bound to the data control. It can now display data from the city field of the Cities table. 12. Place another text box, txtPop1995, on the form. 13. Select txtPop1995’s DataSource property. 14. Click on the down arrow to the right of the Settings box and select datCities. 15. Select the DataField property, click on the down arrow at the right of the Settings box, and select pop1995. 16. Run the program. The form will appear as in Figure 11-1. The arrows on the data control, called navigation arrows, look and act like VCR buttons. The arrows have been identified by the tasks they perform. 17. Click on the various navigation arrows on the data control to see the different cities and their populations in the Cities table displayed in the text boxes. 18. Change the name of a city or change its population and then move to another record. If you look back through the records, you will see that the data have been permanently changed. FIGURE 11-1 A Data Control with Two Text Boxes Bound to It ■ USING CODE WITH A DATA CONTROL Only one record can be accessed at a time; this record is called the current record. In this walkthrough, the text boxes bound to the data control showed the contents of the city and pop1995 fields of the current record. The user clicked on the navigation arrows of the data control to select a new current record. Code can be used to designate another record as the current record. The methods MoveNext, MovePrevious, MoveLast, and MoveFirst select a new current record as suggested by their names. For instance, the statement Data1.Recordset.MoveLast specifies the last record of the table to be the current record. (The word Recordset is inserted in most data-control statements that manipulate records for reasons that needn’t concern us now.) The entry of the field fieldName of the current record is Data1.Recordset.Fields(“fieldName”).Value For instance, with the status as in Figure 11-1, the statement strVar = datCities.Recordset.Fields(“city”).Value An Introduction to Databases 325
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Computer Programming Concepts and V
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CONTENTS SECTION 1: PROBLEM SOLVING
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13.3 WEB PAGE PROGRAMMING WITH VBSC
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S E C T I O N 1 PROBLEM SOLVING
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4 Computer Programming Concepts and
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10 Computer Programming Concepts an
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S E C T I O N 2 FUNDAMENTALS OF PRO
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3.1 SUB PROCEDURES, PART I Structur
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The second task performed by the ad
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‘The density (number of people pe
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"Hawaii", 1184000, 6471 "Alaska", 6
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dure by just using the variable in
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Call CalculateSum(x, y, s) Call Dis
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■ FORM-LEVEL VARIABLES Visual Bas
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3. In Appendix D, the section “St
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Private Sub cmdDetermine_Click() Di
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Private Sub cmdCompute_Click() Dim
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preceded with the word ByVal. Built
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It is clear from the hierarchy char
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The meaningful procedure names, alo
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FIGURE 3-9 Sample Run for Programmi
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4.1 RELATIONAL AND LOGICAL OPERATOR
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(a) (2 < n) And (n < 6) (b) (2 < n)
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SOLUTION: In the following program,
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The Else part of an If block can be
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picTax.Cls picTax.Print “Your FIC
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Case 4, 5 picOutcome.Print “You a
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EXAMPLE 3 The following program use
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Case Else picResult.Print “The st
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4. The items in the value list must
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The hierarchy chart in Figure 4-4 s
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‘Program to compute employees’
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Private Function TaxMarried(adjPay
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and tells us whether the food meets
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S E C T I O N 5 REPETITION
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132 Computer Programming Concepts a
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S E C T I O N 6 ARRAYS
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S E C T I O N 7 SEQUENTIAL FILES
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S E C T I O N 8 RANDOM-ACCESS FILES
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S E C T I O N 9 THE GRAPHICAL DISPL
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Page 295 and 296: 10.1 LIST BOXES AND COMBO BOXES The
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Page 301 and 302: Private Sub cmdDisplay_Click() picF
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Page 309 and 310: THE SHAPE CONTROL The shape control
Page 311 and 312: FIGURE 10-9 A Picture Created with
Page 313 and 314: Rows 9 ScrollBars 0 - flexScrollBar
Page 315 and 316: Private Sub cmdQuit_Click() End End
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Page 379 and 380: ■ EVENTS In the previous section
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Public Function X() As Integer X =
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End Sub Private Sub cmdDropBomb_Cli
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Next i End Sub Public Function Read
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Remove method. The number of object
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S E C T I O N 13 COMMUNICATING WITH
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A P P E N D I C E S
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APPENDIX C VISUAL BASIC STATEMENTS,
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CANCEL The Cancel property provides
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COLS and ROWS The Cols and Rows pro
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DEFINT, DEFLNG, DEFSNG, DEFDBL, DEF
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ENVIRON Visual Basic has an environ
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FONT.ITALIC or FONTITALIC These pro
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yields “1234.”, Format(1234000,
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the length of the string currently
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ISNUMERIC The value of the function
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Unlock statement is used to remove
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Focus Default Default Number First
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OR (Logical Operator) The logical e
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the same as in the original Dimensi
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SECOND The function Second extracts
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STRETCH When the Stretch property o
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UNLOCK The Unlock command is intend
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[COLOR]: Numbers written in base 16
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Appendix D 457
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466 Technology of the Internet D Da
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468 Technology of the Internet Rela
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470 Technology of the Internet 2. D
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SYSTEM REQUIREMENTS CD-ROM INSTRUCT
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Computer Programming Concepts and Visual Basic David I. Schneider

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