Understanding Computer Files - Cengage

Understanding Computer Files - Cengage

Programming Logic and Design Eighth Edition Chapter 7 File Handling and Applications Objectives In this chapter, you will learn about: Computer files The data hierarchy Performing file operations Control break logic Merging files Master and transaction file processing

Random access files Programming Logic and Design, Eighth Edition 2 Understanding Computer Files Computer file A collection of data stored on permanent storage devices such as your computers hard drive, a hard drive on the cloud, DVDs, USB drives, and reels of magnetic tape Text files (numbers, names, salaries) that can be read by a text editor Binary files (images and music)

File size measured in bytes Byte (one character), kilobyte (thousands of bytes), megabyte (millions of bytes), gigabyte (billions of bytes), terabyte (trillions of bytes) Programming Logic and Design, Eighth Edition 3 Understanding Computer Files (continued) Figure 7-1 Three stored files showing their names, dates of modification, type, and

sizes Programming Logic and Design, Eighth Edition 4 Understanding Computer Files (continued) Organizing files Directories and folders Organization units on storage devices

Path Combination of disk drive plus the complete hierarchy of directories Example: C:\Logic\SampleFiles\PayrollData.dat Programming Logic and Design, Eighth Edition 5 Understanding the Data Hierarchy Data hierarchy Describes the relationships between data components Consists of: Characters Letters number and special symbols

Fields Data items representing a single attribute of a record Records Groups of fields that go together for some logical reason Files Groups of related records Programming Logic and Design, Eighth Edition 6 Performing File Operations Use data files in your programs Declaring a file identifier InputFile employeeData OutputFile updatedData

Opening a file open employeeData "EmployeeData.dat" Reading from a file and processing the data input name from employeeData input address from employeeData input payRate from employeeData Programming Logic and Design, Eighth Edition 7 Performing File Operations

(continued) Figure 7-2 How employee data in a readable comma-delimited file might appear in a text reader Programming Logic and Design, Eighth Edition 8 Performing File Operations (continued) Figure 7-3 Reading three data items from a storage device into memory Programming Logic and Design, Eighth Edition

9 Performing File Operations (continued) Sequential file Program reads all the records in this file from beginning to end, processing them one t a time Sorting The process of placing records in order by the value in a specific field or fields

Writing data to a file output name, address, payRate to employeeData Closing a file Always close every file you open Programming Logic and Design, Eighth Edition 10 A Program that Performs File Operations

Figure 7-4 Flowchart and pseudocode for a program that uses files (Continues) Programming Logic and Design, Eighth Edition 11 A Program that Performs File Operations (continued) Backup file - a copy kept in case values need to be restored to their original

state The backup copy is called a parent file and the newly revised copy is a child file Figure 7-4 Flowchart and pseudocode for a program that uses files (continued) Programming Logic and Design, Eighth Edition 12 Understanding Control Break Logic A control break is a temporary detour in the logic of a program A control break program uses a change in a value to initiate special actions or processing

A control break report groups similar data together Input records must be in sequential order Programming Logic and Design, Eighth Edition 13 Understanding Sequential Files and Control Break Logic (continued) Figure 7-5 A control break report with totals after each state Programming Logic and Design, Eighth Edition

14 Understanding 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 and Design, Eighth Edition 15 Understanding Control Break Logic (continued) Single-level control break A detour based on the value of a single variable Uses a control break field to hold the previous value Programming Logic and Design, Eighth Edition 16

Understanding Control Break Logic (continued) Figure 7-6 Mainline logic and getReady() module for the program that produces clients by state report Programming Logic and Design, Eighth Edition 17

Understanding Control Break Logic (continued) Figure 7-7 The produceReport() and controlBreak() modules for the program that produces clients by state Programming Logic and Design, Eighth Edition 18 Understanding Control Break Logic (continued)

Figure 7-8 The finishUp()module for the program that produces clients by state report Programming Logic and Design, Eighth Edition 19 Merging Sequential Files Merging files Combining two or more files while maintaining the sequential order Examples A file of current employees in ID number order, and a file of newly hired employees also in ID number order

A 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 and Design, Eighth Edition 20 Merging Sequential Files (continued) Two conditions required for merging files Each file has the same record layout

Sorted in the same order based on the same field Ascending order (lowest to highest values) Descending order (highest to lowest values) Programming Logic and Design, Eighth Edition 21 Merging Sequential Files Figure 7-9 Sample data contained in two customer files Programming Logic and Design, Eighth Edition

(continued) Figure 7-10 Merged customer file 22 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 and Design, Eighth Edition 23 Merging Sequential Files (continued)

Figure 7-11 Mainline logic of a program that merges files Programming Logic and Design, Eighth Edition 24 Merging Sequential Files (continued) Figure 7-12 The getReady() method for a program that merges files, and the methods it calls (Continues)

Programming Logic and Design, Eighth Edition 25 Merging Sequential Files (continued) Figure 7-12 The getReady() method for a program that merges files, and the methods it calls Programming Logic and Design, Eighth Edition

26 Merging Sequential Files Programming Logic and Design, Eighth Edition (continued) Figure 7-13 Start of merging process 27 Merging Sequential Files

Programming Logic and Design, Eighth Edition (continued) Figure 7-14 Continuation of merging process 28 Merging Sequential Files (continued)

Figure 7-15 The mergeRecords() and finishUp() modules for the file-merging program Programming Logic and Design, Eighth Edition 29 Master and Transaction File Processing Some related files have a master-transaction relationship Master file Holds complete and relatively permanent data

Transaction file Contains temporary data to be used to update the master file Update the master file Changes to values in its fields based on transactions Programming Logic and Design, Eighth Edition 30 Master and Transaction File Processing (continued)

Examples A 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 of every telephone line (number) and a transaction file with information about every call Programming Logic and Design, Eighth Edition 31

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 and Design, Eighth Edition

32 Master and Transaction File Processing (continued) Figure 7-16 Mainline logic for the master-transaction program Programming Logic and Design, Eighth Edition 33 Master and

Transaction File Processing (continued) Figure 7-17 The housekeeping() module for the master-transaction program, and the modules it calls (Continues) Programming Logic and Design, Eighth Edition 34

Master and Transaction File Processing (continued) Figure 7-17 The housekeeping() module for the mastertransaction program, and the modules it calls Programming Logic and Design, Eighth Edition 35 Master and Transaction File

Processing (continued) Figure 7-18 The updateRecords() module for the master-transaction program Programming Logic and Design, Eighth Edition 36 Master and Transaction File Processing (continued)

Figure 7-19 Sample data for the file-matching program Programming Logic and Design, Eighth Edition 37 Master and Transaction File Processing (continued) Figure 7-20 The finishUp() module for the master-transaction program Programming Logic and Design, Eighth Edition

38 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 A program in which the user makes direct requests

Programming Logic and Design, Eighth Edition 39 Random Access Files (continued) Random access files Records can be located in any order Instant access files Locating a particular record directly

Also known as direct access files Programming Logic and Design, Eighth Edition 40 Random Access Files (continued) Figure 7-21 Accessing a record in a sequential file and in a random access file Programming Logic and Design, Eighth Edition

41 Summary Computer file A 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 files combines two or more files Maintains the same sequential order

Programming Logic and Design, Eighth Edition 42 Summary Master files Hold permanent data Updated by transaction files Real-time applications Require random access files Records stored in any order Records accessed immediately

Programming Logic and Design, Eighth Edition 43

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