Programming Logic and
Design
Fifth Edition, Comprehensive
Chapter 1
An Overview of Computers and Logic
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
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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
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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
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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
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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
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Understanding Computer Components
and Operations (continued)
• Machine language: controls the computer’s 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
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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
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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.
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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
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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
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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 user’s functional
job tasks
• Failure to understand the problem is the major cause
of most project failures
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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 deskchecking the logic
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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
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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
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Using Software to Translate the Program
into Machine Language (continued)
Figure 1-1 Creating an executable program
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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
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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)
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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
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Understanding Interactive User Input
(continued)
Figure 1-2 A prompt, response, and output in a command line environment
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Understanding Interactive User Input
(continued)
Figure 1-3 A prompt, response, and output in a GUI environment
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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
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Understanding the Data Hierarchy
and File Input (continued)
Figure 1-4 The data hierarchy
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Understanding the Data Hierarchy
and File Input (continued)
Figure 1-5 The EMPLOYEE file represented as a stack of index cards
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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
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Using Flowchart Symbols and
Pseudocode Statements (continued)
Figure 1-6 Input symbol
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Using Flowchart Symbols and
Pseudocode Statements (continued)
Figure 1-7 Processing symbol
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Using Flowchart Symbols and
Pseudocode Statements (continued)
Figure 1-8 Output symbol
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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
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Using Flowchart Symbols and
Pseudocode Statements (continued)
Figure 1-9 Flowchart and pseudocode of program that doubles a number
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Using Flowchart Symbols and
Pseudocode Statements (continued)
Figure 1-10 Inefficient pseudocode for program that doubles 10,000 numbers
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Using Flowchart Symbols and
Pseudocode Statements (continued)
Figure 1-11 Flowchart of infinite number-doubling program
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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
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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 employee’s last name
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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
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Ending a Program by Using
Sentinel Values (continued)
Figure 1-12 Flowchart of number-doubling program with sentinel value of 0
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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
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Ending a Program by Using Sentinel
Values (continued)
Figure 1-13 Flowchart using eof
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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
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Managing Large Flowcharts
(continued)
Figure 1-14 Flowchart using the connector
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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
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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
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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
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Understanding Data Types (continued)
Table 1-2 Some examples of legal and illegal assignments
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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
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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
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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
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Summary (continued)
• Data hierarchy:
–
–
–
–
–
Character
Field
Record
File
Database
• Flowchart: pictorial representation of program logic
• Variables: named memory locations that contain
values
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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
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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
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