Example File Manipulation in Visual Basic

Size: px

Start display at page:

Download "Example File Manipulation in Visual Basic"

Chester Wood
5 years ago
Views:

1 Example File Manipulation in Visual Basic Obtain the file from your lecturer: Ex-files.vbp Ex-Files.bas Stock.dat Ex-Files.frm ex-files.vbw Prices.dat One of the most important functions of programming is file handling. Files allow data to be stored for later use ( i.e. can be saved, read and updated from day to day) Some definitions: A file is made up of records A record is made up of fields A field is an item of data This example shows a Stock File for a greetings card wholesale company called Budget Cards Ltd. The company buy in cards from manufacturers (Suppliers) and sell them on to high street retail shops. The data stored on file includes: File Structure StockCode Integer Record number - unique key field Description String 15 chars brief description of the card Category String 10 chars category such as Birthday, Christmas, etc. PriceCode String 2 chars price code AA, BB, CC, DD, EE, etc. (see grey box) Unit String 5 chars cards are usually sold in packs or boxes of 5, 10, 20, etc Quantity Integer number of units available (in stock). SupplierCode Integer The code number of the supplier from whom the card are purchased (see grey box). Active String 1 char Y = active record N = non-active(deleted) Additional files will be added later: PriceList to be used to look up the price for the PriceCode Supplier Name, Address and Tel No of supplier A partially completed program should be obtained from your lecturer. The screen and code are listed on the following pages: Note this is a simplified example it does not contain any validation of input. FileHandlinginVB 1

The Module A module is created to define the data type StockRecord Type StockRecord StockCode As Integer Description As String * 15 Category As String * 10 PriceCode As String * 2 Quantity As Integer

2 The Module A module is created to define the data type StockRecord Type StockRecord StockCode As Integer Description As String * 15 Category As String * 10 PriceCode As String * 2 Quantity As Integer Unit As String * 8 SupplierCode As Integer Active As String * 1 End Type The variable StkRec is declared to be type StockRecord in the main program. Data from the screen is copied to StkRec and then written to the file as a block of data. The Main Form txtdisplay txtstockcode txtdescription txtcategory txtpricecode txtquantity txtunit txtsuppliercode cmdaddrecord cmddelete cmdsearch cmdupdate cmdclose CmdListFile cmdundelete cmdsaveupdate cmdclear FileHandlinginVB 2

3 Code Option Explicit 'General Declarations Dim StkRec As StockRecord Dim WkRec As StockRecord Dim UpdateRecNo As Integer 'used in UpdateRecord and SaveUpdated StkRec has the same format as StockRecord defined in the module. Private Sub cmdaddrecord_click() Dim OutMsg As String * 25 Dim RecNo As Integer User enters data to the boxes on screen then hits the Add Record button. If txtstockcode = "" Then MsgBox "You must enter a Stock Code" RecNo = Val(txtStockCode) 'check to see if record already on file Get #1, RecNo, WkRec If WkRec.Active = "Y" Then MsgBox "Record already on file" 'write record to file StkRec.StockCode = txtstockcode StkRec.Description = txtdescription StkRec.Category = txtcategory StkRec.PriceCode = txtpricecode StkRec.Quantity = txtquantity StkRec.Unit = txtunit StkRec.SupplierCode = txtsuppliercode StkRec.Active = "Y" Put #1, RecNo, StkRec Using the StockCode as the record number the file is checked to see if a record already exists (and is active) before allowing the new record to be written. The data is copied from the screen text boxes into the StkRec area and then written to the file by the put #1 statement. Note that the Active field is set to Y for new records. End Sub OutMsg = "Record " + Str(StkRec.StockCode) + " written" MsgBox (OutMsg) FileHandlinginVB 3

4 Private Sub cmdlistfile_click() Dim x As Integer PicDisplay.Cls PicDisplay.Print Tab(0); "Stock"; Tab(8); "Description"; Tab(25); _ "Category"; Tab(40); "Price"; Tab(50); _ "Quantity"; Tab(60); "Unit"; Tab(68); _ "Supplier"; Tab(78); "Active" PicDisplay.Print Tab(0); "code"; Tab(40); "Code"; Tab(68); "Code" x = 1 While Not EOF(1) Get #1, x, StkRec If StkRec.Active = "Y" Or StkRec.Active = "N" Then The Display is cleared. The headings are written. Tab( ) moves across the screen. PicDisplay.Print Tab(0); StkRec.StockCode; Tab(8); StkRec.Description; _ Tab(25); StkRec.Category; Tab(40); StkRec.PriceCode; Tab(50); _ StkRec.Quantity; Tab(60); StkRec.Unit; Tab(68);_ StkRec.SupplierCode; Tab(78); StkRec.Active x = x + 1 Wend End Sub The WHILE loop ends when the End Of File (EOF) is reached. X is used to count through the records in the file. Get reads a record into the StkRec. By removing the bolded text from the IF only active records will be shown!!! There are already a few records on the file. Click on the list button and write them in the table below Stock Code Description Category PriceCode Quantity Unit Supplier Code Active FileHandlinginVB 4

5 Exercise 1 Convert the algorithm below to create the code for the Delete Button: Delete Record Data Received : StockCode {the user should have entered a Stock Code var OutMsg var RecNo var Reply String[30] Integer String Begin End If StockCode is empty Then Error Message "You must enter a StockCode" RecNo = Value (StockCode) { check to see if record is on file } Read Stock Record at position RecNo from Stock file {Get #1, RecNo, StkRec If StkRec.Active = "N" Then Error Message "Record not on file" {Display Record to confirm delete Display StockRecord {copy record to text boxes Display Confirm Delete Input Reply If Reply = Yes Then 'Mark record as deleted (not Active) StkRec.Active = "N" Write Stock Record to File at RecNo position {Put #1, RecNo, StkRec Display message Record StockCode Deleted. Test the new button by deleting a record and listing the file. Note that the Active field changes to N for deleted records. Test the Undelete button by undeleting a record you have deleted. Note that the Active field changes to Y for records not deleted. FileHandlinginVB 5

6 Exercise 2 Convert the Structure chart below to create the Search Button Search StockCode = Empty True Error Must enter Stock Code Set RecNo = StockCode Read record at RecNo Record = Deleted True Error Record Not on File Display Record Details Perform a search for records you have on file. Check that records marked as deleted are not displayed by the search. FileHandlinginVB 6

7 Exercise 3 A second file is to be included to keep track of price codes (i.e. look up the price that matches the Price Code). The file is on disk as Prices.dat It has the following record structure: PriceCode string 2 chars Store the Price Code Price currency Store the Price 1) Define a suitable data type in the visual basic module. 2) Declare the record in the General Declarations of the Form. Call it PriceRec. 3) Open the file as #2 in Form Load ( ) 4) Add a new text box next to Form. Place it next to the Price Code text box as shown below: Category txtprice Price Code Quantity Price 5) Now write code to look up the price as the user enters a Price Code. In the Validation for the PriceCode text box add the following code: Found=false x = 1 While NOT EOF(2) and NOT Found Read PriceRec from Prices File If txtpricecode = PriceRec.PriceCode then Found = true Endif x = x + 1 Wend If Found then TxtPrice = PriceRec.Price Msgbox Invalid Price Code. Please re-enter. Endif Prices File Data on the prices file: Test this new validation check is working. This lookup will also be useful in other buttons/subrouotines. PriceCode Price AA 1.50 BB 2.00 CC 2.25 FileHandlinginVB 7

WebStore. Resellers. Brief User Guide. Invite. Self-Register. Log-In. Lost Password. Support. SIPHON 31 May Resellers must be invited to use

WebStore. Resellers. Brief User Guide. Invite. Self-Register. Log-In. Lost Password. Support. SIPHON 31 May Resellers must be invited to use Resellers WebStore Brief User Guide Invite Resellers must be invited to use the SIPHON WebStore. This is important as we need to approve your email address against your account. If you would like to register