Computer Programming Concepts and Visual Basic David I. Schneider

UNLOCK The Unlock command is intended for use in programs that operate on a network.
After a Lock statement has been used to deny access to all or part of a file (see the discussion
of Lock for details), a corresponding Unlock statement can be used to restore access.
Suppose a data file has been opened as reference number n. The locks established by the
statements Lock #n; Lock #n, r1; and Lock #n, r1 To r2 are undone by the statements Unlock
#n; Unlock #n, r1; and Unlock #n, r1 To r2, respectively. There must be an exact correspondence
between the locking and the unlocking statements used in a program, that is, each set
of paired statements must refer to the same range of record numbers or bytes.
UPDATE The Update method of a data control is used to save changes made to the database.
VAL The Val function is used to convert strings to numbers. If the leading characters of the
string str corresponds to a number, then Val(str) will be the number represented by these
characters. For any number n, Val(Str(n)) is n.
VALIDATE The Validate event procedure is activated whenever the current record of a database
table is about to be changed. The heading of the procedure has the form Private Sub
Data1_Validate(Action As Integer, Save As Integer), where 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 convert one
operation into another.
VALUE The Value property of a scroll bar is a number between the values of the Min and
Max properties of the scroll bar that is related to the position of the thumb. The Value property
of an option button is True when the button is on and False when the button is off. The
Value property of a check box is 0 (unchecked), 1 (checked), or 2 (grayed). The Value property
of Fields(“fieldName”) reads the contents of a field of the current record.
VARIANT A variable of type variant can be assigned numbers, strings, and several other
types of data. Variant variables are written without type-declaration tags. [variant]
VARTYPE The value of the function VarType(var) is a number indicating the type of value
stored in var. This function is primarily used to check the type of data stored in a variant variable.
Some values returned by VarType are 0 for “Empty,” 1 for “Null,” 2 for Integer, 3 for
Long Integer, 4 for Single Precision, 5 for Double Precision, 6 for Currency, 7 for Date, 8 for
String, 9 for OLE Automation object, 10 for Error, 11 for Boolean, 13 for Non-OLE Automation
object, and 17 for Byte. For nonvariant arrays, the number assigned is 8192 plus the
number assigned to the type of the array. [variant]
VISIBLE The property Visible determines whether or not a form or control is displayed. If
the Visible property of an object is True, the object will be displayed (if not covered by other
objects) and respond to events if its Enabled property is True. If the Visible property of an
object is set to False, the object will not be displayed and cannot respond to events.
WEEKDAY The value of the function WeekDay(d) is a number giving the day of the week
for the date store in d. These values will range from 1 for Sunday to 7 for Saturday.
WHILE/WEND A While ... Wend loop is a sequence of statements beginning with a statement
of the form While condition and ending with the statement Wend. After the While statement
is executed, the computer repeatedly executes the entire sequence of statements inside
the loop as long as the condition is true.
WIDTH (Property) The property Width determines the horizontal size of an object. Width
is measured in units of twips. For the Printer object, Width may be read (pw = Printer.Width
is OK) but not assigned (Printer.Width = 100 causes an error).
WIDTH (Statement) If s is an integer less than 255 and n is the reference number of a file
opened in sequential mode, the statement Width #n, s causes Visual Basic to permit at most
s characters to be printed on a single line in the file. Visual Basic will send a carriagereturn/line-feed
pair to the file after s characters have been printed on a line, even if the Print
# or Write # statement would not otherwise start a new line at that point. The statement Width
Appendix C 453