Visual Basic.NET How to Program (PDF)

Chapter 17 Files and Streams 831
17.2 a) 1s, 0s. b) bit. c) file. d) characters. e) database. f) ReadLine. g) WriteLine.
h) Stream, Object. i) System.IO. j) System.Runtime.Serialization.Formatters.Binary.
EXERCISES
17.3 Create a program that stores student grades in a text file. The file should contain the name,
ID number, class taken and grade of every student. Allow the user to load a grade file and display its
contents in a read-only textbox. The entries should be displayed as follows:
LastName, FirstName: ID# Class Grade
We list some sample data below:
Jones, Bob: 1 "Introduction to Computer Science" "A-"
Johnson, Sarah: 2 "Data Structures" "B+"
Smith, Sam: 3 "Data Structures" "C"
17.4 Modify the previous program to use objects of class that can be serialized to and deserialized
from a file. Ensure fixed-length records by fixing the length of fields LastName, FirstName,
Class and Grade.
17.5 Extend classes StreamReader and StreamWriter. Allow the class that derives from
StreamReader to have methods ReadInteger, ReadBoolean and ReadString. Allow the
class that derives from StreamWriter to have methods WriteInteger, WriteBoolean and
WriteString. Think about how to design the writing methods so that the reading methods will be
able to read what was written. Design WriteInteger and WriteBoolean to write Strings of
uniform size so that ReadInteger and ReadBoolean can read those values accurately. Make
sure ReadString and WriteString use the same character(s) to separate Strings.
17.6 Create a program that combines the ideas of Fig. 17.9 and Fig. 17.11 to allow the user to
write records to and read records from a file. Add an extra field of type Boolean to the record indicating
whether the account has overdraft protection.
17.7 In commercial data processing, it is common to have several files in each application system.
In an accounts-receivable system, for example, there is generally a master file containing detailed information
about each customer, such as the customer’s name, address, telephone number, outstanding
balance, credit limit, discount terms, contract arrangements and possibly a condensed history of recent
purchases and cash payments.
As transactions occur (i.e., sales are made and cash payments arrive in the mail), they are entered
into a file. At the end of each business period (i.e., a month for some companies, a week for
others and a day in some cases), the file of transactions (trans.dat) is applied to the master file
(oldmast.dat), thus updating each account’s record of purchases and payments. During an updating
run, the master file is rewritten as a new file (newmast.dat), which then is used at the end of
the next business period to begin the updating process again.
File-matching programs must deal with certain problems that do not exist in single-file programs.
For example, a match does not always occur. A customer on the master file might not have
made any purchases or cash payments in the current business period, and, therefore, no record for this
customer will appear on the transaction file. Similarly, a customer who did make some purchases or
cash payments might have just moved to the community, and the company might not have had a
chance to create a master record for this customer.
When a match occurs (i.e., records with the same account number appear on both the master
file and the transaction file), add the dollar amount on the transaction file to the current balance on
the master file and write the newmast.dat record. (Assume that purchases are indicated by positive