Programming Logic and Design Fifth Edition, Comprehensive

1
Programming Logic and Design Fifth Edition,
Comprehensive

• Chapter 1
• An Overview of Computers and Logic

2
Objectives

• Understand computer components and operations
• Learn about the steps involved in the programming
  process
• Learn about the data hierarchy and file input
• Use flowchart symbols and pseudocode statements
• Use and name variables

3
Objectives (continued)

• Use a sentinel, or dummy value, to end a program
• Manage large flowcharts
• Assign values to variables
• Recognize the proper format of assignment
  statements
• Describe data types
• Understand the evolution of programming
  techniques

4
Understanding Computer Components and Operations

• Hardware and software the two major components
  of any computer system
• Hardware equipment, or devices
• Software programs that contain instructions for
  the computer
• Four major operations in a computer
• Input
• Processing
• Output
• Storage

5
Understanding Computer Components and Operations
(continued)

• Input devices allow data to enter the computer
• Mouse, keyboard, scanner
• Processing working on the data
• Organizing data
• Checking data for accuracy
• Mathematical or other manipulations on data
• Central Processing Unit (CPU) hardware that
  performs the tasks

6
Understanding Computer Components and Operations
(continued)

• Output devices provide data to the user
• Printer, monitor, speakers
• Programming language special language containing
  instructions for the computer
• Visual Basic, Java, C, C, COBOL
• Syntax rules governing word usage and
  punctuation in the language

7
Understanding Computer Components and Operations
(continued)

• Machine language controls the computers on/off
  circuitry
• Compiler or interpreter software that translates
  programming languages to machine language
• Program must be free of syntax errors to be run,
  or executed, on a computer
• To function properly, the logic must be correct

8
Understanding Computer Components and Operations
(continued)

• What is wrong with this logic for making a cake?
• Stir
• Add two eggs
• Bake at 350 degrees for 45 minutes
• Add three cups of flour

9
Understanding Computer Components and Operations
(continued)

• Logic errors, or semantic errors, are more
  difficult to locate than syntax errors
• Logic for multiplying a number by 2 (includes
  input, processing, and output statements)
• Get input number.
• Compute calculated answer as
• inputNumber times 2.
• Print calculatedAnswer.

10
Understanding Computer Components and Operations
(continued)

• Two storage categories internal and external
• Internal storage
• Main memory, random access memory (RAM)
• Located inside the computer system
• Volatile contents are lost when power goes down
• External storage
• Persistent contents are relatively permanent
• Floppy drive, hard drive, flash media, magnetic
  tape
• Located outside the computer system

11
Understanding the Programming Process

• Six programming phases
• Understand the problem
• Plan the logic
• Code the program
• Use software to translate the program to machine
  language
• Test the program
• Put the program into production

12
Understanding the Problem

• May be the most difficult phase
• Users may not be able to articulate their needs
  well
• User needs may be changing frequently
• Programmers may have to learn the users
  functional job tasks
• Failure to understand the problem is the major
  cause of most project failures

13
Planning the Logic

• Plan the steps that the program will take
• Use tools such as flowcharts and pseudocode
• Flowchart a pictorial representation of the
  logic steps
• Pseudocode Natural language representation of
  the logic
• Walk through the logic before coding by
  desk-checking the logic

14
Coding the Program

• Select the programming language
• Some languages more efficient for certain tasks
• All languages handle input, arithmetic
  processing, output, other standard functions
• Logic can be executed in any number of languages
• Write the instructions
• Planning generally more difficult than coding

15
Using Software to Translate the Program into
Machine Language

• Programmers write instructions in high-level
  languages that resemble a natural language
• Compilers or interpreters change the programs
  into a low-level machine language that can be
  executed
• Syntax errors are identified by the compiler or
  interpreter

16
Using Software to Translate the Program into
Machine Language (continued)
Figure 1-1 Creating an executable program
17
Testing the Program

• Execute it with sample data and check results
• Identify logic errors and correct them
• Choose test data carefully to exercise all
  branches of the logic

18
Putting the Program into Production

• Might mean simply running the program once
• Process might take months if program is used on
  regular basis or is part of larger development
• Train data-entry people and users
• Change existing data
• Conversion entire set of actions organization
  must take to switch over to new program(s)

19
Understanding Interactive User Input

• Prompt message displayed on a monitor
• Asks the user for a response
• Command prompt location to type entries to
  communicate with the operating system
• Graphical User Interface (GUI) allows users to
  interact with a program in a graphical environment

20
Understanding Interactive User Input (continued)
Figure 1-2 A prompt, response, and output in a
command line environment
21
Understanding Interactive User Input (continued)
Figure 1-3 A prompt, response, and output in a
GUI environment
22
Understanding the Data Hierarchy and File Input

• Data hierarchy ordering of data types by size
• Character single symbol
• A, 7,
• Field group of characters forming a single data
  item
• Smith
• Record a group of related fields
• Customer record containing name and address
  fields
• File a group of related records
• Customer file, containing all customer records
• Database collection of related files, called
  tables, that serve the information needs of the
  organization

23
Understanding the Data Hierarchy and File Input
(continued)
Figure 1-4 The data hierarchy
24
Understanding the Data Hierarchy and File Input
(continued)
Figure 1-5 The EMPLOYEE file represented as a
stack of index cards
25
Using Flowchart Symbols and Pseudocode Statements

• Flowchart pictorial representation of the logic
• Pseudocode English-like representation of the
  logic
• Example
• start
• get inputNumber
• compute calculatedAnswer as
• inputNumber times 2
• print calculatedAnswer
• stop

26
Using Flowchart Symbols and Pseudocode Statements
(continued)
Figure 1-6 Input symbol
27
Using Flowchart Symbols and Pseudocode Statements
(continued)
Figure 1-7 Processing symbol
28
Using Flowchart Symbols and Pseudocode Statements
(continued)
Figure 1-8 Output symbol
29
Using Flowchart Symbols and Pseudocode Statements
(continued)

• Flowlines
• Connect the steps
• Show the sequence of statements
• Have arrows to show the direction
• Terminal symbol (start/stop symbol)
• Shows the start and end points of the statements
• Lozenge shape

30
Using Flowchart Symbols and Pseudocode Statements
(continued)
Figure 1-9 Flowchart and pseudocode of program
that doubles a number
31
Using Flowchart Symbols and Pseudocode Statements
(continued)
Figure 1-10 Inefficient pseudocode for program
that doubles 10,000 numbers
32
Using Flowchart Symbols and Pseudocode Statements
(continued)
Figure 1-11 Flowchart of infinite
number-doubling program
33
Using and Naming Variables

• Variable a memory location whose contents can
  vary also called an identifier
• Each programming language has its own rules for
  naming identifiers, including
• Legal characters
• Maximum length
• Use of upper- or lowercase
• Variable name must be a single word, but can be
  formed from several words
• rate, interestRate, interest_rate

34
Using and Naming Variables (continued)

• Choose meaningful names for variables
• Improves the readability and maintainability of
  code

Table 1-1 Suitability of suggested variable
names for an employees last name
35
Ending a Program by Using Sentinel
Values

• Infinite loop a sequence of statements that
  repeats forever with no escape
• Avoid infinite loops by testing for a
  predetermined value that means stop processing
• Decision testing a value
• Flowchart decision symbol a diamond shape with
  two flowlines, one for Yes and one for No

36
Ending a Program by Using Sentinel Values
(continued)
Figure 1-12 Flowchart of number-doubling program
with sentinel value of 0
37
Ending a Program by Using Sentinel Values
(continued)

• Sentinel value (or dummy value)
• Does not represent real data
• Signal to stop
• Can be used with input from files or from users
• End-of-file (EOF) marker
• Code stored in the file that marks the end of the
  data
• Usually used instead of a sentinel value for file
  input

38
Ending a Program by Using Sentinel Values
(continued)
Figure 1-13 Flowchart using eof
39
Managing Large Flowcharts

• Flowchart connector symbol
• Marks a logic transfer to another location in the
  flowchart
• Transfer location can be on the same page or on
  another page
• On-page symbol a circle with a number or letter
  to identify the matching transfer location
• Off-page symbol a square with a pointed bottom,
  containing page number and a number of letter to
  identify the matching transfer location

40
Managing Large Flowcharts (continued)
Figure 1-14 Flowchart using the connector
41
Assigning Values to Variables

• Assignment statement
• Assigns a value to a variable
• Variable must appear on the left side, value on
  the right side of the assignment operator
• Right side may be an expression that will be
  evaluated before storing the value in the
  variable
• Assignment operator the equal sign () in most
  languages
• Variable
• Memory location has an address and a value
• Value (contents) is used for various operations

42
Understanding Data Types

• Two basic data types
• Text
• Numeric
• Numeric data stored by numeric variables
• Text data stored by string, text, or character
  variables
• Constants
• Values that do not change while the program is
  running
• Have identifiers, and can be used like variables
  for calculations, but cannot be assigned new
  values

43
Understanding Data Types (continued)

• Some programming languages implement several
  numeric data types, such as
• Integer whole numbers only
• Floating-point fractional numeric values with
  decimal points
• Character or string data is represented as
  characters enclosed in quotation marks
• x, color
• Data types must be used appropriately

44
Understanding Data Types (continued)
Table 1-2 Some examples of legal and illegal
assignments
45
Understanding the Evolution of Programming
Techniques

• Programming began in the 1940s, using memory
  addresses and machine code directly
• Higher-level languages were developed to allow
  English-like instructions
• Older programs were monolithic, and ran from
  beginning to end
• Newer programs contain modules that can be
  combined to form programs

46
Understanding the Evolution of Programming
Techniques (continued)

• Two major programming techniques
• Procedural programming
• Object-oriented programming
• Procedural programming focuses on the procedures
  that programmers create
• Object-oriented programming focuses on objects
  that represent real-world things and their
  attributes and behaviors
• Both techniques employ reusable program modules

47
Summary

• Four major computer operations
• Input
• Processing
• Output
• Storage
• Six programming phases
• Understand the problem
• Plan the logic
• Code the program
• Translate the program to machine language
• Test the program
• Deploy the program

48
Summary (continued)

• Data hierarchy
• Character
• Field
• Record
• File
• Database
• Flowchart pictorial representation of program
  logic
• Variables named memory locations that contain
  values

49
Summary (continued)

• Testing a value involves making a decision
• Assignment statements store a value into a
  variable
• Assignment operator the equal () sign in most
  languages

50
Summary (continued)

• Two major data types text and numeric
• Procedural programming focuses on actions
  performed on data
• Object-oriented programming focuses on
  representing and manipulating objects