Random File: Program Code ( visual basic )

Computer Science(9608) notes and Resources

Imports System.IO

Module Module1

    Structure employeerecord

        <VBFixedString(15)> Dim firstname As String

        <VBFixedString(15)> Dim lastname As String

        <VBFixedString(15)> Dim title As String

    End Structure

    Dim employee As employeerecord

    Dim filenumber As Integer

    Dim lastrec As Integer

    Dim position As Integer

    Dim reclength As Long = Len(employee)

    Dim deleted As Boolean = False

    Function randomgetlastrecord() As Integer

        filenumber = FreeFile()

        FileOpen(filenumber, "d:/employee.txt", OpenMode.Random, , , reclength)

        Dim lastrecord As Long

        lastrecord = 1

        Do While Not (EOF(filenumber))

            FileGet(filenumber, employee, lastrecord)

            lastrecord = lastrecord + 1

        Loop

        FileClose(filenumber)

       Return lastrecord

    End Function

    Sub randominputintofile()

        Dim employeefirstname As String

        Dim employeelastname As String

        Dim employeetitle As String

        Dim i As Integer

        For i = 1 To 3

            lastrec = randomgetlastrecord()

            filenumber = FreeFile()

            FileOpen(filenumber, "d:/employee.txt", OpenMode.Random, , , reclength)

            Console.WriteLine("enter firstname")

            employeefirstname = Console.ReadLine()

            Console.WriteLine("enter lastname")

            employeelastname = Console.ReadLine()

            Console.WriteLine("enter title")

            employeetitle = Console.ReadLine()

            employee.firstname = employeefirstname

            employee.lastname = employeelastname

            employee.title = employeetitle

            FilePut(filenumber, employee, lastrec)

            FileClose(filenumber)

        Next

    End Sub

    Sub randomgetfromfile()

        filenumber = FreeFile()

        FileOpen(filenumber, "d:/employee.txt", OpenMode.Random, , , reclength)

        position = 1

        Do While Not EOF(filenumber)

            FileGet(filenumber, employee, position)

            Console.WriteLine(employee.firstname & " " & employee.lastname & " " & employee.title)

            position = position + 1

        Loop

        FileClose(filenumber)

    End Sub

    Sub randomsearchrecord()

        Dim sname As String

        Console.WriteLine("enter name to search")

        sname = Console.ReadLine()

        filenumber = FreeFile()

        Dim found As Boolean = False

        FileOpen(filenumber, "d:/employee.txt", OpenMode.Random, , , reclength)

        Do While Not EOF(filenumber) And found = False

            FileGet(filenumber, employee, )

            If (Trim(employee.firstname) = sname) Then

                position = Loc(filenumber)

                found = True

            End If

        Loop

        If found = True Then

            Console.WriteLine("record found at position " & position)

            deleted = True

        Else

            Console.WriteLine("no record exits ")

        End If

        FileClose(filenumber)

    End Sub

    Sub randomupdaterecord()

        randomsearchrecord()

        Console.WriteLine("required position is " & position)

        filenumber = FreeFile()

        FileOpen(filenumber, "d:/employee.txt", OpenMode.Random, , , reclength)

        Seek(filenumber, position)

        employee.lastname = "dangol"

        employee.title = "lecturer"

        FilePut(filenumber, employee, )

        FileClose(filenumber)

    End Sub

    Sub randomdeleterecord()

        randomsearchrecord()

        Dim filenumber1, filenumber2 As Integer

        filenumber1 = FreeFile()

        FileOpen(filenumber1, "d:/employee.txt", OpenMode.Random, , , reclength)

        filenumber2 = FreeFile()

        FileOpen(filenumber2, "d:/employeenew.txt", OpenMode.Random, , , reclength)

        Do While Not EOF(filenumber1)

            If (Loc(filenumber1) <> position - 1) Then

                FileGet(filenumber1, employee, )

                FilePut(filenumber2, employee, )

            Else

                FileGet(filenumber1, employee, )

            End If

        Loop

        FileClose(filenumber1)

        FileClose(filenumber2)

        Kill("d:/employee.txt")

        Rename("d:/employeenew.txt", "d:/employee.txt")

        If deleted = True Then

            Console.WriteLine("Record deleted successfully")

        End If

    End Sub

    Sub Main()

        Console.WriteLine("Random file handling")

        Console.WriteLine("")

        Console.WriteLine("enter 1 to add record")

        Console.WriteLine("")

        Console.WriteLine("enter 2 to list record")

        Console.WriteLine("")

        Console.WriteLine("enter 3 to search record")

        Console.WriteLine("")

        Console.WriteLine("enter 4 to edit record")

        Console.WriteLine("")

        Console.WriteLine("enter 5 to delete record")

        Console.WriteLine("")

        Dim choice As Integer

        Console.WriteLine("ENTER YOUR CHOICE")

        choice = Console.ReadLine()

        Select Case choice

            Case 1

                randominputintofile()

            Case 2

                randomgetfromfile()

            Case 3

                randomsearchrecord()

            Case 4

                randomupdaterecord()

            Case 5

                randomdeleterecord()

            Case Else

                Console.WriteLine("invalid entry")

        End Select

        Console.ReadLine()

     End Sub

End Module

                                                           - CIE A-LEVEL COMPUTER SCIENCE (  9608 )

Exception handling

Computer Science(9608) notes and Resources





Exception: An exception is a problem that occurs during the execution of a program due to unforeseen circumstances such as an attempt to divide by zero while the program is running.

 Exception handling: Exception handling is a mechanism in which a programming construct is ‘used to consistently trap, intercept and handle the error occurred during application execution

Advantages of Exception Handling

•      Exception handling allows us to control the normal flow of the program by using  exception handling in program.

•      It throws an exception whenever a calling method encounters an error providing that the calling method takes care of that error.

•      It also gives us the scope of organizing and differentiating between different errors types using a separate block of codes. This is done with the help of try-catch blocks.

•      Provides a type-safe, integrated approach for coping with the unusual predictable problem that arises while executing program.

•      Provide means to detect and report an “exceptional circumstance” so  that appropriate action can be taken

•      Easy identification of program code and error handling code (separating error handling code from “regular” code)

•      Meaningful error reporting

•      Grouping error types and error differentiation

•      Increased reliability and better performance

Module Module1

    Sub Main()

        Dim num1, num2 As Integer

        Console.WriteLine("Enter any number: ")

        num1 = Console.ReadLine()

        Console.WriteLine("Again enter any number: ")

        num2 = Console.ReadLine()

        Console.WriteLine("numberator/denominator = " & (num1 / num2))

        Console.ReadLine()

    End Sub

End Module

 If the user enter value 6 for num1 and value 3 for num2, the answer is 2

 If the user enter value 0 for num2, the answer is infinity

 If a user enters a char or any string value., the program crashes

To solve any unforeseen event, the try catch block can be used

Module Module1

    Sub Main()

        Dim num1, num2 As Integer

        Try

            Console.WriteLine("Enter any number: ")

            num1 = Console.ReadLine()

            Console.WriteLine("Again enter any number: ")

            num2 = Console.ReadLine()

            Console.WriteLine("numberator/denominator = " & (num1 / num2))

        Catch ex As Exception

            Console.writeline("Invalid input")

        End Try

        Console.ReadLine()

    End Sub

End Module

Now, the problem is resolved and the user is informed about the wrong input.

Importance of exception handling: To make sure that program always run smoothly and does not crash any event.


                                                           - CIE A-LEVEL COMPUTER SCIENCE (  9608 )

Serial File: Program code ( visual basic )

Computer Science(9608) notes and Resources

Writing records to file

Module Module1

    Sub Main()

        Dim sw As IO.StreamWriter

        sw = IO.File.CreateText("d:/staff.txt")

        sw.WriteLine("ram 100")

        sw.WriteLine("shyam 200")

        sw.WriteLine("hari 300")

        sw.WriteLine("sita 400")

        sw.WriteLine("gita 500")

        sw.Close()

        Console.ReadLine()

    End Sub

End Module

Appending records to file

Module Module1

    Sub Main()

        Dim sw As IO.StreamWriter

        sw = IO.File.AppendText("d:/staff.txt")

        sw.WriteLine("ramesh 600")

        sw.WriteLine("suresh 700")

        sw.WriteLine("gopal 800")

        sw.Close()

        Console.ReadLine()

    End Sub

End Module

Reading all records from file

Imports System.IO

Module Module1

    Sub Main()

        Dim staffdtl As String

        Dim sr As StreamReader

        sr = File.OpenText("d:/staff.txt")

        Do Until sr.Peek = -1

            staffdtl = sr.ReadLine()

            Console.WriteLine(staffdtl)

        Loop

        sr.Close()

        Console.ReadLine()

    End Sub

End Module

Searching name in the list

Imports System.IO

Module Module1

    Sub Main()

        Dim staffdtl As String

        Dim found As Boolean = False

        Dim breakvalue() As String

        Dim sr As StreamReader

        sr = File.OpenText("d:/staff.txt")

        Dim sname As String

        Console.WriteLine("enter name to search")

        sname = Console.ReadLine()

        Do Until sr.Peek = -1

            staffdtl = sr.ReadLine()

            breakvalue = staffdtl.Split(" ")

            If breakvalue(0) = sname Then

                found = True

            End If

        Loop

        sr.Close()

        If found = True Then

            Console.WriteLine(sname & " exists in the list")

        Else

            Console.WriteLine("no record exists")

        End If

        Console.ReadLine()

    End Sub

End Module

Deleting record from a file

Imports System.IO

Module Module1

    Sub Main()

        Dim staffdtl As String

        Dim breakvalue() As String

        Dim sr As StreamReader

        sr = File.OpenText("d:/staff.txt")

        Dim sw As StreamWriter

        sw = File.CreateText("d:/staffnew.txt")

        Dim sname As String

        Console.WriteLine("enter name to delete")

        sname = Console.ReadLine()

     

        Do Until sr.Peek = -1

            staffdtl = sr.ReadLine()

            breakvalue = staffdtl.Split(" ")

            If breakvalue(0) <> sname Then

                sw.WriteLine(staffdtl)

            End If

        Loop

        sw.Close()

        sr.Close()

        File.Delete("d:/staff.txt")

        File.Move("d:/staffnew.txt", "d:/staff.txt")

        Console.ReadLine()

    End Sub

End Module

                                                           - CIE A-LEVEL COMPUTER SCIENCE (  9608 )

STACK: Program code ( visual basic )

Computer Science(9608) notes and Resources

STACK: A Stack has a Last In First Out ( LIFO ) data structure, i.e., the last element to enter would be the first one to be processed.

Implementation of Stack in Visual basic.

Module Module1

    Dim item As String

    Dim top As Integer

    Dim arraystack(10) As String

    Sub Main()

        Dim tempItem As String

        Dim counter As Integer

        Dim choice As Integer

        createEmptyStack()

        Do

            Console.WriteLine("Select any option: ")

            Console.WriteLine("  1. Inserting items in Stack")

            Console.WriteLine("  2. Deleting an item in stack")

            Console.WriteLine("  3. Searching an item in stack")

            Console.WriteLine("  4. Making stack empty")

            Console.WriteLine("  5. Listing all the itms from stack")

            Console.WriteLine("  0. Exit")

            Console.Write("     =>  ")

            choice = Console.ReadLine()

            Select Case choice

                Case 1

                    Console.WriteLine()

                    Console.WriteLine(" Enter item: ")

                    Console.Write("     => ")

                    tempItem = Console.ReadLine()

                    insertItemStack(tempItem)

                    Console.Clear()

                Case 2

                    removeItemStack()

                    Console.Clear()

                Case 3

                    Console.Clear()

                    Console.Write(" Enter an item to be searched: ")

                    tempItem = Console.ReadLine()

                    findItem(tempItem)

                    Console.Clear()

                Case 4

                    createEmptyStack()

                    Console.Clear()

                Case 5

                    Console.Clear()

                    If top = 0 Then

                        Console.WriteLine(" Stack is empty")

                    Else

                        For counter = top To 1 Step -1

                            Console.WriteLine(arraystack(counter))

                        Next

                    End If

                    Console.ReadKey()

                    Console.Clear()

            End Select

        Loop Until choice = 0

    End Sub

    Sub createEmptyStack()

        top = 0

    End Sub

    Sub insertItemStack(ByVal InsertItem As String)

        If top = arraystack.Length() - 1 Then

            Console.WriteLine("Stack is full")

        Else

            top = top + 1

            arraystack(top) = InsertItem

            Console.WriteLine(InsertItem & " inserted into sack")

            Console.WriteLine()

            Console.WriteLine(" Press any key to continue....")

        End If

        Console.ReadKey()

    End Sub

    Sub removeItemStack()

        If top = 0 Then

            Console.WriteLine("Stack is empty")

        Else

            item = arraystack(top)

            top = top - 1

            Console.WriteLine(item & " has been deleted")

            Console.WriteLine()

            Console.WriteLine(" Press any key to continue....")

        End If

        Console.ReadKey()

    End Sub

    Sub findItem(ByVal searchItem As String)

        Dim count As Integer

        For count = top To 1 Step -1

            If arraystack(count) = searchItem Then

                Console.WriteLine(searchItem & " is found at position " & count)

                Console.WriteLine()

                Console.WriteLine(" Press any key to continue....")

            End If

        Next

        Console.ReadKey()

    End Sub

End Module

                                                           - CIE A-LEVEL COMPUTER SCIENCE (  9608 )