Programming Logic and Design Sixth Edition Chapter 7

Programming Logic and Design Sixth Edition Chapter 7 File Handling and Applicaitons

Objectives In this chapter, you will learn about: • Computer files • The data hierarchy • Performing file operations • Sequential files and control break logic • Merging sequential files Programming Logic & Design, Sixth Edition 2

Objectives (continued) • Master and transaction file processing • Random access files Programming Logic & Design, Sixth Edition 3

Understanding Computer Files • Random access memory (RAM) – Temporary storage – Example: storing a value in a variable – Volatile storage • Permanent storage – Nonvolatile storage – Example: saving a program to disk Programming Logic & Design, Sixth Edition 4

Understanding Computer Files (continued) • Computer file – Collection of data stored on a nonvolatile device – Exists on permanent storage devices – Types • Text • Binary – Characteristics • Name • Time of creation and last modified • Size measured in bytes Programming Logic & Design, Sixth Edition 5

Organizing Files • Directories and folders – Organization units on storage devices • Path – Combination of the disk drive plus the complete hierarchy of directories in which a file resides – C: LogicSample. FilesPayroll. Data. dat Programming Logic & Design, Sixth Edition 6

Understanding the Data Hierarchy • Data hierarchy – Describes the relationships between data components – Consists of: • • Characters Fields Records Files Programming Logic & Design, Sixth Edition 7

Performing File Operations • Use data files in your programs – Declaring a file Input. File employee. Data Output. File updated. Data – Opening a file open employee. Data "Employee. Data. dat" – Reading from a file input name from employee. Data input address from employee. Data input pay. Rate from employee. Data Programming Logic & Design, Sixth Edition 8

Performing File Operations(continued) Figure 7 -2 Reading three data items from a storage device into memory Programming Logic & Design, Sixth Edition 9

Performing File Operations(continued) – Writing to a file output name, address, pay. Rate to updated. Data – Closing a file Programming Logic & Design, Sixth Edition 10

Figure 7 -3 Flowchart and pseudocode for program that uses a file Programming Logic & Design, Sixth Edition 11

Figure 7 -3 Flowchart and pseudocode for program that uses a file (continued) Programming Logic & Design, Sixth Edition 12

A Program that Performs File Operations • Backup file – Copy that is kept in case values need to be restored to their original state – Called a parent file – Newly revised copy is a child file Programming Logic & Design, Sixth Edition 13

Understanding Sequential Files and Control Break Logic • Sequential file – Records are stored one after another in some order • Control break – Temporary detour in the logic of a program Programming Logic & Design, Sixth Edition 14

Understanding Sequential Files and Control Break Logic (continued) • Control break program – Change in the value of a variable initiates special actions or causes special or unusual processing to occur – Single-level control break – Control break field Programming Logic & Design, Sixth Edition 15

Understanding Sequential Files and Control Break Logic (continued) Figure 7 -4 A control break report with totals after each state Programming Logic & Design, Sixth Edition 16

Understanding Sequential Files and Control Break Logic (continued) • Examples of control break reports – All employees listed in order by department number, with a new page started for each department – All books for sale in a bookstore listed in order by category (such as reference or self-help), with a count following each category of book – All items sold in order by date of sale, with a different ink color for each new month Programming Logic & Design, Sixth Edition 17

Figure 7 -5 Mainline logic and get. Ready() module for the program that produces clients by state report Programming Logic & Design, Sixth Edition 18

Figure 7 -6 The produce. Report() and control. Break() modules for the program that produces clients by state Programming Logic & Design, Sixth Edition 19

Figure 7 -7 The finish. Up() module for the program that produces clients by state report Programming Logic & Design, Sixth Edition 20

Merging Sequential Files • Merging files – Combining two or more files while maintaining the sequential order • Examples – File of current employees in ID number order and a file of newly hired employees, also in ID number order – File of parts manufactured in the Northside factory in part-number order and a file of parts manufactured in the Southside factory, also in part-number order Programming Logic & Design, Sixth Edition 21

Merging Sequential Files (continued) • Two conditions required for merging files – Each file has same record layout – Sorted in the same order based on the same field Programming Logic & Design, Sixth Edition 22

Merging Sequential Files (continued) Figure 7 -8 Sample data contained in two customer files Programming Logic & Design, Sixth Edition 23

Merging Sequential Files (continued) Figure 7 -9 Merged customer file Programming Logic & Design, Sixth Edition 24

Merging Sequential Files (continued) • Mainline logic similar to other file-processing programs, except for handling two files • With two input files, must determine when both files are at eof – Define a flag variable to indicate that both files have reached eof – Must define two input files – Read one record from each input file Programming Logic & Design, Sixth Edition 25

Figure 7 -10 Mainline logic of a program that merges files Programming Logic & Design, Sixth Edition 26

Figure 7 -12 Start of the merging process Programming Logic & Design, Sixth Edition 27

Figure 7 -13 Continuation of development of merging process Programming Logic & Design, Sixth Edition 28

Master and Transaction File Processing • Some related files have a master-transaction relationship • Master file – Holds relatively permanent data • Transaction file – Contains temporary data to be used to update the master file • Update the master file Programming Logic & Design, Sixth Edition 29

Master and Transaction File Processing (continued) • Examples – Library maintains a master file of all patrons and a transaction file with information about each book or other items checked out – A college maintains a master file of all students and a transaction file for each course registration – A telephone company maintains a master file for every telephone line (number) and a transaction file with information about every call Programming Logic & Design, Sixth Edition 30

Master and Transaction File Processing (continued) • Updating approaches – Change information in master file – Copy master file and change new version • Begin with both files sorted in the same order on the same field Programming Logic & Design, Sixth Edition 31

Figure 7 -16 The housekeeping() module for master-transaction program and the modules it calls Programming Logic & Design, Sixth Edition 32

Figure 7 -17 The update. Records() module for the master-transaction program Programming Logic & Design, Sixth Edition 33

Master and Transaction File Processing (continued) Figure 7 -18 Sample data for the file-matching program Programming Logic & Design, Sixth Edition 34

Random Access Files • Batch processing – Involves performing the same tasks with many records, one after the other – Uses sequential files • Real-time applications – Require that a record be accessed immediately while a client is waiting • Interactive program – Program in which the user makes direct requests Programming Logic & Design, Sixth Edition 35

Random Access Files (continued) • Random access files – – – Records can be located in any order Instant access files Direct access files Declare Seek Programming Logic & Design, Sixth Edition 36

Summary • Computer file – Collection of data stored on a nonvolatile device in a computer system • Data items are stored in a hierarchy • Using a data file – Declare, open, read, write, close • Sequential file: records stored in some order • Merging sequential files – Master-transaction files • Random access files Programming Logic & Design, Sixth Edition 37