Computer Programming Concepts and Visual Basic David I. Schneider

Recommendations

Info

326 Computer Programming Concepts and Visual Basic assigns “Beijing” to the variable strVar and the statements datCities.Recordset.Edit datCities.Recordset.Fields(“city”).Value = “Peking” datCities.Recordset.Update change the city field of the current record to “Peking”. (The first statement makes a copy of the current record for editing. The second statement alters the copy, and the third statement sends the new copy of the record to the database.) The number of previously accessed records in the table is given by the RecordCount property. The EOF (End Of File) and BOF (Beginning Of File) run-time properties indicate whether the end or beginning of the file has been reached. For instance, the following two sets of statements each place the cities into a list box. datCities.Recordset.MoveLast ‘Needed to set value of RecordCount datCities.Recordset.MoveFirst For i = 1 to datCities.Recordset.RecordCount lstBox.AddItem datCities.Recordset.Fields(“city”).Value datCities.Recordset.MoveNext Next i datCities.Recordset.MoveFirst Do While Not datCities.Recordset.EOF lstBox.AddItem datCities.Recordset.Fields(“city”).Value datCities.Recordset.MoveNext Loop The current record can be marked for removal with the statement Data1.Recordset.Delete The record will be removed when a data control navigation arrow is clicked or a Move method is executed. A new record can be added to the end of the table with the statement Data1.Recordset.AddNew followed by Data1.Recordset.Fields(“fieldName”).Value = entryForField statements for each field and a Data1.Recordset.Update statement. Alternately, the AddNew method can be followed by the user typing the information into text boxes bound to the data control and then moving to another record. (Note: When you add a record and then click on the MovePrevious arrow, you will not see the next-to-last record, but rather will see the record preceding the record that was current when AddNew was executed.) ■ THE VALIDATION EVENT Visual Basic has a device called validation that lets you restrict the values a user can enter into a table. For instance, if the Cities table is only to contain cities with a population of more than 1 million, you can use validation to prevent any record with a number less than 1 in the pop1995 field from being entered. Validation also allows you to catch (and prevent) errors that might cause a program to crash. Data controls have an event procedure called Validate that is activated whenever the current record is about to be changed. For instance, it is called when a navigation arrow is
clicked or a Move, Update, Delete, or AddNew method is executed. The general form of the Validate event procedure is Private Sub Data1_Validate(Action As Integer, Save As Integer) statement(s) End Sub The value of Action identifies the specific operation that triggered the event and the value of Save specifies whether data bound to the control has changed. You can change the value of the Action argument to perform a different action. Some values of the Action argument are shown in Table 11.3. TABLE 11.3 Some Values of the Action Argument Value Description 1 MoveFirst method 2 MovePrevious method 3 MoveNext method 4 MoveLast method 5 AddNew method 6 Update operation (not UpdateRecord) 7 Delete method 10 Close method If you assign 0 to the Action argument, the operation will be canceled when the Validate event procedure is exited. The value of Save is –1 (True) if the data in any control attached to the data control have changed and is 0 (False) otherwise. If you set the value of Save to 0 in the Validate event procedure, any changes will not be saved. Consider the form created in the walkthrough. Suppose the contents of txtPop1995, the 1995 population text box, is changed to .8 and then a navigator arrow is clicked in an attempt to move to another record. The following code prevents the move. Private Sub datCities_Validate(Action As Integer, Save As Integer) Dim strMsg As String If val(txtPop1995) < 1 then strMsg = “We only allow cities having a population ” & _ “at least one million.” MsgBox strMsg“City too small!” Action = 0 End If End Sub If the statement Action = 0 is changed to Save = 0 the move will take place, but the previous record will retain its original values. That is, the number .8 will not appear in the table. EXAMPLE 1 An Introduction to Databases 327 The following program is a general database manager for the Cities table in the MEGACTY1.MDB database. It allows the user to edit the Cities table as needed and to locate information based on the city name. (In the Validate event procedure, the inner If block keeps the message box from appearing when the first or last record is deleted.)
Page 1 and 2:
Computer Programming Concepts and V
Page 3 and 4:
CONTENTS SECTION 1: PROBLEM SOLVING
Page 5:
13.3 WEB PAGE PROGRAMMING WITH VBSC
Page 9:
S E C T I O N 1 PROBLEM SOLVING
Page 12 and 13:
4 Computer Programming Concepts and
Page 14 and 15:
Page 16 and 17:
Page 18 and 19:
10 Computer Programming Concepts an
Page 20 and 21:
Page 23:
S E C T I O N 2 FUNDAMENTALS OF PRO
Page 26 and 27:
Page 28 and 29:
Page 30 and 31:
Page 32 and 33:
Page 34 and 35:
Page 36 and 37:
Page 38 and 39:
Page 40 and 41:
Page 42 and 43:
Page 44 and 45:
Page 46 and 47:
Page 48 and 49:
Page 50 and 51:
Page 52 and 53:
Page 54 and 55:
Page 56 and 57:
Page 58 and 59:
Page 60 and 61:
Page 62 and 63:
Page 64 and 65:
Page 66 and 67:
Page 68 and 69:
Page 70 and 71:
Page 72 and 73:
Page 74 and 75:
Page 76 and 77:
Page 78 and 79:
Page 81 and 82:
3.1 SUB PROCEDURES, PART I Structur
Page 83 and 84:
The second task performed by the ad
Page 85 and 86:
‘The density (number of people pe
Page 87 and 88:
"Hawaii", 1184000, 6471 "Alaska", 6
Page 89 and 90:
dure by just using the variable in
Page 91 and 92:
Call CalculateSum(x, y, s) Call Dis
Page 93 and 94:
■ FORM-LEVEL VARIABLES Visual Bas
Page 95 and 96:
3. In Appendix D, the section “St
Page 97 and 98:
Private Sub cmdDetermine_Click() Di
Page 99 and 100:
Private Sub cmdCompute_Click() Dim
Page 101 and 102:
preceded with the word ByVal. Built
Page 103 and 104:
It is clear from the hierarchy char
Page 105 and 106:
The meaningful procedure names, alo
Page 107:
FIGURE 3-9 Sample Run for Programmi
Page 111 and 112:
4.1 RELATIONAL AND LOGICAL OPERATOR
Page 113 and 114:
(a) (2 < n) And (n < 6) (b) (2 < n)
Page 115 and 116:
SOLUTION: In the following program,
Page 117 and 118:
The Else part of an If block can be
Page 119 and 120:
picTax.Cls picTax.Print “Your FIC
Page 121 and 122:
Case 4, 5 picOutcome.Print “You a
Page 123 and 124:
EXAMPLE 3 The following program use
Page 125 and 126:
Case Else picResult.Print “The st
Page 127 and 128:
4. The items in the value list must
Page 129 and 130:
The hierarchy chart in Figure 4-4 s
Page 131 and 132:
‘Program to compute employees’
Page 133 and 134:
Private Function TaxMarried(adjPay
Page 135 and 136:
and tells us whether the food meets
Page 137:
S E C T I O N 5 REPETITION
Page 140 and 141:
132 Computer Programming Concepts a
Page 142 and 143:
Page 144 and 145:
Page 146 and 147:
Page 148 and 149:
Page 150 and 151:
Page 152 and 153:
Page 154 and 155:
Page 156 and 157:
Page 158 and 159:
Page 160 and 161:
Page 162 and 163:
Page 164 and 165:
Page 167:
S E C T I O N 6 ARRAYS
Page 170 and 171:
Page 172 and 173:
Page 174 and 175:
Page 176 and 177:
Page 178 and 179:
Page 180 and 181:
Page 182 and 183:
Page 184 and 185:
Page 186 and 187:
Page 188 and 189:
Page 190 and 191:
Page 192 and 193:
Page 194 and 195:
Page 196 and 197:
Page 198 and 199:
Page 200 and 201:
Page 202 and 203:
Page 204 and 205:
Page 206 and 207:
Page 208 and 209:
Page 210 and 211:
Page 212 and 213:
Page 214 and 215:
Page 216 and 217:
Page 218 and 219:
Page 220 and 221:
Page 223:
S E C T I O N 7 SEQUENTIAL FILES
Page 226 and 227:
Page 228 and 229:
Page 230 and 231:
Page 232 and 233:
Page 234 and 235:
Page 236 and 237:
Page 238 and 239:
Page 240 and 241:
Page 242 and 243:
Page 244 and 245:
Page 246 and 247:
Page 248 and 249:
Page 251:
S E C T I O N 8 RANDOM-ACCESS FILES
Page 254 and 255:
Page 256 and 257:
Page 258 and 259:
Page 260 and 261:
Page 262 and 263:
Page 265:
S E C T I O N 9 THE GRAPHICAL DISPL
Page 268 and 269:
Page 270 and 271:
Page 272 and 273:
Page 274 and 275:
Page 276 and 277:
Page 278 and 279:
Page 280 and 281:
Page 282 and 283:
Page 284 and 285: 276 Computer Programming Concepts a
Page 295 and 296: 10.1 LIST BOXES AND COMBO BOXES The
Page 297 and 298: Private Sub cmdAdd_Click() Dim item
Page 299 and 300: either typing in information or jus
Page 301 and 302: Private Sub cmdDisplay_Click() picF
Page 303 and 304: clicks on the square to toggle betw
Page 305 and 306: circle and the button is said to be
Page 307 and 308: hsbBar.Value changes accordingly. T
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
Page 317 and 318: Here, the menu bar contains two men
Page 319 and 320: Clipboard.Clear deletes the content
Page 321 and 322: cedures that are available to all f
Page 323 and 324: The Flags property influences certa
Page 325 and 326: 13. Additional forms serve as new w
Page 327: 6. Voting Machine. The members of t
Page 331 and 332: 11.1 AN INTRODUCTION TO DATABASES T
Page 333: 9. Click on the down arrow to the r
Page 337 and 338: Do While (Not foundFlag) And (Not d
Page 339 and 340: mary key. Databases of student enro
Page 341 and 342: question mark stands for a single c
Page 343 and 344: 1995 populations. When the second c
Page 345 and 346: If a Find method does not locate a
Page 347 and 348: place an x in the check box next to
Page 349 and 350: population (in descending order). W
Page 351 and 352: Creating and Designing Databases 34
Page 353 and 354: 9. When all fields have been specif
Page 355 and 356: Creating and Designing Databases 34
Page 357 and 358: TABLE 11.5(B) TABLE 11.5(C) course
Page 359: (a) Update the quantity field of th
Page 363 and 364: 12.1 CLASSES AND OBJECTS noun A wor
Page 365 and 366: Task Statement Assign a value to a
Page 367 and 368: EXAMPLE 1 and then an instance of t
Page 369 and 370: [Run, enter the data for a student
Page 371 and 372: SOLUTION: Object Property Setting f
Page 373 and 374: 4. Methods can be either Function o
Page 375 and 376: ‘Student Class (CStudent) Private
Page 377 and 378: txtFinal.Text = “” picGrades.Pr
Page 379 and 380: ■ EVENTS In the previous section
Page 381 and 382: frmCircles.ForeColor = vbRed ‘Mak
Page 383 and 384: Public Function X() As Integer X =
Page 385 and 386:
End Sub Private Sub cmdDropBomb_Cli
Page 387 and 388:
Next i End Sub Public Function Read
Page 389 and 390:
Remove method. The number of object
Page 391:
S E C T I O N 13 COMMUNICATING WITH
Page 394 and 395:
Page 396 and 397:
Page 398 and 399:
Page 400 and 401:
Page 402 and 403:
Page 404 and 405:
Page 406 and 407:
Page 408 and 409:
Page 410 and 411:
Page 413:
A P P E N D I C E S
Page 416 and 417:
Page 418 and 419:
Page 420 and 421:
Page 422 and 423:
Page 424 and 425:
Page 426 and 427:
Page 428 and 429:
Page 431 and 432:
APPENDIX C VISUAL BASIC STATEMENTS,
Page 433 and 434:
CANCEL The Cancel property provides
Page 435 and 436:
COLS and ROWS The Cols and Rows pro
Page 437 and 438:
DEFINT, DEFLNG, DEFSNG, DEFDBL, DEF
Page 439 and 440:
ENVIRON Visual Basic has an environ
Page 441 and 442:
FONT.ITALIC or FONTITALIC These pro
Page 443 and 444:
yields “1234.”, Format(1234000,
Page 445 and 446:
the length of the string currently
Page 447 and 448:
ISNUMERIC The value of the function
Page 449 and 450:
Unlock statement is used to remove
Page 451 and 452:
Focus Default Default Number First
Page 453 and 454:
OR (Logical Operator) The logical e
Page 455 and 456:
the same as in the original Dimensi
Page 457 and 458:
SECOND The function Second extracts
Page 459 and 460:
STRETCH When the Stretch property o
Page 461 and 462:
UNLOCK The Unlock command is intend
Page 463 and 464:
[COLOR]: Numbers written in base 16
Page 465 and 466:
Appendix D 457
Page 467 and 468:
Page 469 and 470:
Page 471 and 472:
Page 473 and 474:
Page 475 and 476:
466 Technology of the Internet D Da
Page 477 and 478:
468 Technology of the Internet Rela
Page 479 and 480:
470 Technology of the Internet 2. D
Page 481:
SYSTEM REQUIREMENTS CD-ROM INSTRUCT
show all

Computer Programming Concepts and Visual Basic David I. Schneider

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?