Computer Programming Concepts and Visual Basic David I. Schneider

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440 Computer Programming Concepts and Visual Basic right with spaces and assigned to var. If var has a user-defined type, then expr must be of the same type. The statement var = expr is equivalent to Let var = expr. LINE The graphics method objectName.Line (x1, y1)–(x2, y2) draws a line connecting the two points. The graphics method objectName.Line –(x2, y2) draws a line from the point (objectName.CurrentX, objectName.CurrentY) to the specified point. The object object- Name can be a form, picture box, or the Printer. The line is in color c if objectName.Line (x1, y1)–(x2, y2), c is executed. The statement objectName.Line (x1, y1)–(x2, y2), ,B draws a rectangle with the two points as opposite vertices. (If B is replaced by BF, a solid rectangle is drawn.) After a Line method is executed, the value of objectName.CurrentX becomes x2 and the value of objectName.CurrentY becomes y2. [color] [coordinate systems] LINE INPUT # After a file has been opened as a sequential file for Input with reference number n, the statement Line Input #n, str assigns to the string variable str the string of characters from the current location in the file up to the next pair of carriage return/line feed characters. LIST The List property of a combo box, directory list box, drive list box, file list box, or list box is used to access items in the list. When one of these controls is created, Visual Basic automatically creates the string array List to hold the list of items stored in the control. The value of List1.List(n) is the item of List1 having index n. The value of List1.List (List1.ListIndex) is the item (string) currently highlighted in list box List1. LISTCOUNT For a list or combo box, the value of List1.ListCount or Combo1.ListCount is the number of items currently in the list. For a directory list box, drive list box, or file list box, the value of control.ListCount is the number of subdirectories in the current directory, the number of drives on the computer, or the number of files in the current directory that match the Pattern property, respectively. LISTINDEX The ListIndex property gives the index of the currently selected item is a combo box, directory list box, drive list box, file list box, or list box. LOAD The Load event applies only to forms and usually occurs only once, immediately when a program starts. This is the appropriate place to put code that should be executed every time a program is run, regardless of the user’s actions. LOAD If controlName is the name of a control in a control array whose Index property was assigned a value during form design and num is a whole number that has not yet been used as an index for the controlName() array, then the statement Load controlName(num) copies properties of controlName(0) and creates the element controlName(num) of the control- Name() array. LOADPICTURE The statement objectName.Picture = LoadPicture(pictureFile), where objectName is a form or picture box, places the picture defined in the file specified by pictureFile on objectName. LOC This function gives the current location in a sequential, random-access, or binary file. For a sequential file with reference number n, Loc(n) is the number of blocks of 128 characters read from or written to the file since it was opened. For a random-access file, Loc(n) is the current record (either the last record read or written, or the record identified in a Seek statement). For a binary file, Loc(n) is the number of bytes from the beginning of the file to the last byte read or written. For communications, the value of Loc(n) is the number of bytes waiting in the communications buffer with reference number n. [binary file] LOCK The Lock command is intended for use in programs that operate on a network. After a file has been opened with reference number n, the statement Lock #n denies access to the file by any other process. For a random-access file, the statement Lock #n, r1 To r2 denies access to records r1 through r2 by any other process. For a binary file, this statement denies access to bytes r1 through r2. The statement Lock #n, r1 locks only record (or byte) r1. For a sequential file, all forms of the Lock statement have the same effect as Lock #n. The
Unlock statement is used to remove locks from files. All locks should be removed before a file is closed or the program is terminated. [binary file] LOF After a file has been opened with reference number n, the number of characters in the file (that is, the length of the file) is given by LOF(n). For communications, the value of LOF(n) equals the number of bytes waiting in the communications buffer with reference number n. LOG If x is a positive number, the value of Log(x) is the natural logarithm (base e) of x. LONG A variable of type Long requires 4 bytes of memory and can hold the whole numbers from –2,147,483,648 to 2,147,483,647. Long values and variables may be indicated by the type tag &: 12345678&, Population&. LOSTFOCUS A LostFocus event occurs when an object loses the focus, either through a user action or through code, via the SetFocus method. LSET If strVar is a string variable, then the statement LSet strVar = str replaces the value of strVar with a string of the same length consisting of str truncated or padded on the right with spaces. LSet also can be used to assign a record of one user-defined type to a record of a different user-defined type. LTRIM The value of the function LTrim(str) is the string obtained by removing all the spaces from the beginning of the string str. The string str may be either of fixed or variable length. MAX and MIN The Max and Min properties of scroll bars give the values of horizontal (vertical) scroll bars when the thumb is at the right (bottom) and left (top) arrows, respectively. MAXBUTTON The MaxButton property determines whether or not a form has a Maximize button in the upper-right corner. If the value of the MaxButton property is set to True (the default), a Maximize button is displayed when the program is run. The user then has the option to click on the Maximize button to cause the form to enlarge and fill the entire screen. If the value of the MaxButton property is set to False, the maximize button is not displayed when the program is run, and the user is thus unable to “maximize” the form. MAXLENGTH The property MaxLength determines the maximum number of characters that a text box will accept. If the MaxLength property for a text box is set to 0 (the default), an unlimited number of characters may be entered in the text box. MID The value of the function Mid(str, m, n) is the substring of str beginning with the mth character of str and containing up to n characters. If the parameter n is omitted, Mid(str, m) is all the characters of str from the mth character on. The statement Mid(str, m, n) = str2 replaces the characters of str, beginning with the mth character, by the first n characters of the string str2. MINBUTTON The MinButton property determines whether or not a form has a Minimize button in the upper-right corner. If the value of the MinButton property is set to True (the default), a Minimize button is displayed when the program is run. The user then has the option to click on the Minimize button to cause the form to be replaced by a small icon in the Taskbar at the bottom of the screen. If the value of the MinButton property is set to False, the Minimize button is not displayed when the program is run, and the user is thus unable to “minimize”the form. MINUTE The function Minute extracts the minutes from a serial date. If d is any valid serial date, the value of Minute(d) is a whole number from 0 to 59 giving the minutes recorded as part of the date and time stored in d. [date] MKDIR The statement MkDir path\dirName creates a subdirectory named dirName~ in the directory specified by path. [directories] Appendix C 441
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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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10.1 LIST BOXES AND COMBO BOXES The
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Private Sub cmdAdd_Click() Dim item
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either typing in information or jus
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Private Sub cmdDisplay_Click() picF
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clicks on the square to toggle betw
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circle and the button is said to be
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hsbBar.Value changes accordingly. T
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THE SHAPE CONTROL The shape control
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FIGURE 10-9 A Picture Created with
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Rows 9 ScrollBars 0 - flexScrollBar
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Private Sub cmdQuit_Click() End End
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Here, the menu bar contains two men
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Clipboard.Clear deletes the content
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cedures that are available to all f
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The Flags property influences certa
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13. Additional forms serve as new w
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6. Voting Machine. The members of t
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11.1 AN INTRODUCTION TO DATABASES T
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9. Click on the down arrow to the r
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clicked or a Move, Update, Delete,
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Do While (Not foundFlag) And (Not d
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mary key. Databases of student enro
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question mark stands for a single c
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1995 populations. When the second c
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If a Find method does not locate a
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place an x in the check box next to
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population (in descending order). W
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Creating and Designing Databases 34
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9. When all fields have been specif
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Creating and Designing Databases 34
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TABLE 11.5(B) TABLE 11.5(C) course
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(a) Update the quantity field of th
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12.1 CLASSES AND OBJECTS noun A wor
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Task Statement Assign a value to a
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EXAMPLE 1 and then an instance of t
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[Run, enter the data for a student
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SOLUTION: Object Property Setting f
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4. Methods can be either Function o
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‘Student Class (CStudent) Private
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txtFinal.Text = “” picGrades.Pr
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■ EVENTS In the previous section
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frmCircles.ForeColor = vbRed ‘Mak
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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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Page 413: A P P E N D I C E S
Page 431 and 432: APPENDIX C VISUAL BASIC STATEMENTS,
Page 433 and 434: CANCEL The Cancel property provides
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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
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Computer Programming Concepts and Visual Basic David I. Schneider

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