Q(uick)BASIC Statement: MOVEPREVIOUS
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MOVEFIRST, MOVELAST, MOVENEXT, MOVEPREVIOUS
Statements that allow you to make records current according to their relative position on the current index in an ISAM table
Worth knowing
Useful and cross-version information about the programming environments of QBasic and QuickBasic.
Syntax
- MOVEFIRST [#]filenumber%
- MOVELAST [#]filenumber%
- MOVENEXT [#]filenumber%
- MOVEPREVIOUS [#]filenumber%
Description/Parameter(s)
- The argument filenumber% is the number used in the OPEN statement to open the table.
MOVEFIRST | First record becomes current. |
MOVELAST | Last record becomes current. |
MOVENEXT | Next record becomes current. |
MOVEPREVIOUS | Previous record becomes current. |
Usage Notes
- The action of the MOVEFIRST, MOVELAST, MOVENEXT, and MOVEPREVIOUS statements is made relative to the current record, according to the current index.
- Using MOVEPREVIOUS when the first record is current moves the current position to the beginning of the table. The beginning of an ISAM table is the position before the first record according to the current index.
- Using MOVENEXT when the last record is current moves the current position to the end of the table. The end of an ISAM table is the position following the last record according to the current index.
Example
This example uses the CREATEINDEX, SETINDEX and DELETEINDEX statements to index an ISAM file in several ways. It displays records from the file using the GETINDEX$ and BOF functions and the MOVEdest statements.
Note: To run this program, you must load the ISAM TSR program PROISAMD.EXE. Also, this program assumes a file called BOOKS.MDB exists in the current directory. BOOKS.MDB is a sample ISAM file that SETUP copies to your disk.
If this program is interrupted before the database is closed, the file BOOKS.MDB may be left in an inconsistent state.
DEFINT A-Z
TYPE BookRec
IDNum AS DOUBLE 'Unique ID number for each book.
Price AS CURRENCY 'Book's price.
Edition AS INTEGER 'Book's edition
Title AS STRING * 50 'Book's title.
Publisher AS STRING * 50 'Book's publisher.
Author AS STRING * 36 'Book's author.
END TYPE
DIM Library AS BookRec 'Record structure variable.
DIM msgtxt AS STRING
CONST Database = "books.mdb" 'Name of the disk file.
CONST TableName = "Bookstock" 'Name of the table.
tablenum = FREEFILE 'File number.
OPEN Database FOR ISAM BookRec TableName AS tablenum
CREATEINDEX tablenum, "A", 0, "Author"
CREATEINDEX tablenum, "I", 1, "IDnum"
CREATEINDEX tablenum, "T", 0, "Title"
CREATEINDEX tablenum, "C", 0, "Price"
'Display static instructions.
CLS : LOCATE 13, 30
PRINT "Choose a key:"
PRINT SPC(9); "Move to:"; TAB(49); "Order by: X"
PRINT : PRINT SPC(9); "F - First record"; TAB(49); "A - Author"
PRINT : PRINT SPC(9); "L - Last record"; TAB(49); "I - ID Number"
PRINT : PRINT SPC(9); "N - Next record"; TAB(49); "T - Title"
PRINT : PRINT SPC(9); "P - Previous record"; TAB(49); "C - Cost"
PRINT : PRINT SPC(9); "Q - Quit"; TAB(49); "X - No order"
LOCATE 3, 1: PRINT TAB(37); "Books"
PRINT STRING$(80, "-");
VIEW PRINT 5 TO 10 'Set viewport for displaying records.
MOVEFIRST tablenum
DO
'Display current record.
CLS
RETRIEVE tablenum, Library
PRINT "Author: "; Library.Author;
PRINT TAB(49); "ID #"; Library.IDNum
PRINT "Title: "; Library.Title
PRINT "Publisher: "; Library.Publisher
PRINT "Cost: "; Library.Price
PRINT SPC(30); msgtxt
PRINT STRING$(64, "-");
IF GETINDEX$(tablenum) = "" THEN
PRINT STRING$(15, "-");
ELSE
PRINT "Index in use: "; GETINDEX$(tablenum);
END IF
'Get keystroke from user.
validkeys$ = "FLNPQATICX"
DO
Keychoice$ = UCASE$(INKEY$)
LOOP WHILE INSTR(validkeys$, Keychoice$) = 0 OR Keychoice$ = ""
msgtxt = ""
'Move to appropriate record, or change indexes.
SELECT CASE Keychoice$
CASE "F"
MOVEFIRST tablenum
CASE "L"
MOVELAST tablenum
CASE "N"
MOVENEXT tablenum
IF EOF(tablenum) THEN
MOVELAST tablenum
BEEP: msgtxt = "** At last record **"
END IF
CASE "P"
MOVEPREVIOUS tablenum
IF BOF(tablenum) THEN
MOVEFIRST tablenum
BEEP: msgtxt = "** At first record **"
END IF
CASE "Q"
EXIT DO
CASE ELSE 'User chose an index.
VIEW PRINT
LOCATE 13, 59: PRINT Keychoice$;
VIEW PRINT 5 TO 10
IF Keychoice$ = "X" THEN Keychoice$ = ""
SETINDEX tablenum, Keychoice$
MOVEFIRST tablenum
END SELECT
LOOP
'User wants to quit, so reset viewport, delete indexes and close files.
VIEW PRINT
DELETEINDEX tablenum, "A"
DELETEINDEX tablenum, "I"
DELETEINDEX tablenum, "T"
DELETEINDEX tablenum, "C"
CLOSE
END
See also: