Programming Logic and Designi
Preface
This book can be used in a stand-alone logic course or as a companion book to an
introductory programming text using any programming language.
 Chapter 1 introduces concepts
 Chapter 2 discusses key concepts of structure
 Chapter 3 extends the structure discussion to modules
 Chapter 4 creates complete structured business programs
 Chapter 5 explores decision-making and Boolean logic
 Chapter 6 discusses looping
 Chapter 7 introduces control breaks
 Chapter 8 introduces arrays
 Chapter 9 deals with arrays used for sorting
 Chapter 10 explores interactive programming using menus
 Chapter 11 covers matching and sequential processing
 Chapter 12 addresses object-oriented programming
 Chapter 13 addresses event-driven programming and GUI
 Chapter 14 addresses good programming design in terms of reducing coupling
and increasing cohesion
 Chapter 15 provides an introduction to UML, a graphical tool for designing
object-oriented systems
Each chapter includes
 Objectives: A useful study aid
 Tips: Alternatives methods and terms
 Summaries: Recaps the programming concepts and techniques covered
 Exercises: Exercises increasing in difficulty designed to provide additional
practice in skills and concepts
Chapter One: An Overview of Computers and Logic
Objectives:
1.
2.
3.
4.
5.
6.
7.
8.
Understand components and operations
Describe programming process
Describe data hierarchy
Understand flowchart symbols
Understand pseudocode statements
Use and name variables
Understand sentinel variables
Describe data types
Key terms:
Data: facts entering the computer system
CPU: Hardware that organizes data, checks for accuracy, performs mathematical
calculations on data
Programming Language: Basic, Visual Basic, Pascal, COBOL, RPG, C#, C++, Java,
Fortran
Syntax: rules governing word usage and punctuation
Compiler (or Interpreter): software to translate the specific programming language into
the computer’s on-off circuitry language
Machine Code: the computer’s on-off circuitry language
Logic (of a program): the instructions given to a computer in a specific sequence
Algorithm: the steps necessary to solve any problem
Conversion: the entire set of actions an organization must take to switch over to using a
new program
Flowcharts: pictorial representation of the logical steps it takes to solve a problem
Pseudocode: an English-like representation of the steps it takes to solve a problem
Variables: memory locations whose contents can vary or differ over time
Decision: testing a value
Dummy Variable: pre-selected value that stops execution of a program
EOF: end of file (of data)
Constants: named memory location, the value of which never changes during a program
(numeric or string)
Computer System Components
1. Hardware: equipment or devices associated with a computer
2. Software: instructions that tell the computer what to do
Major Operations
1.
2.
3.
4.
Input
Processing
Output
Storage
Every computer operates on circuitry that consists of millions of on-off switches
The compiler or interpreter tells you if you have used a programming language
incorrectly
For a program to work correctly, you must not leave any instructions out or add
extraneous instructions
Logic errors are much more difficult to locate than syntax errors
Once instructions have been input to the computer and translated to machine language, a
program can be run or executed.
Computers often have several input devices such as a keyboard, a mouse, a CD drive or a
disk drive
Disk and CD drives are often categorized as storage rather than input devices
Storage
1) Internal storage
a) Memory
i) Main memory / primary memory
2) External storage
a) Floppy disk
b) Hard drive
c) Magnetic tape
Internal memory is volatile, i.e. contents are lost every time the computer loses power
External storage is permanent, i.e. non-volatile storage
Computer memory consists of millions of numbered locations where data can be stored
Programming Steps
1)
2)
3)
4)
5)
6)
7)
8)
Understand the problem
Plan the logic – developing an algorithm
Code the program
Translate the program into machine language
Test the program
Put the program into production
Maintaining a program
Retiring a program
Understanding the problem may be one of the most difficult aspects of programming:
 The description of what the user needs may be vague
 User may not know what it is he or she wants
Planning the logic entails deciding on the steps to include and how to order them
 Utilizes flowcharts or pseudo-code
 Is more difficult than coding the program
Compilers and interpreters translate high-level languages into low-level languages, i.e.
machine language
A program that is free of syntax errors is not necessarily free of logical errors
Programs should be tested with many sets of data
 Many companies don’t know that their software has a problem until an unusual
circumstance occurs
Maintenance is necessary for a number of reasons
1) Changes in the environment
2) Changes in specifications
3) Formats of input change
4) Errors are found
Data Hierarchy






Bits
Bytes
Characters – smallest usable unit of data
Fields – a single data item
Records – logical groupings of fields
Files – logical grouping of records


Tables – groups of files that together serve the needs an organization
Databases – organized groupings of files in table form
Using pseudocode is similar to writing final statements in a programming language
Flowcharts allow a programmer to more easily visualize how the program statements will
connect
Programmers seldom create both pseudocode and a flowchart for the same program
Almost every program involves the steps of input, processing and output
When you crate a flowchart, you draw geometric shapes around the individual statements
and connect them with arrows
 A parallelogram represents input
 A rectangle represents processing, i.e. such as performing arithmetical
calculations
 Parallelograms are also used for output
 A terminal or start/stop symbol is used at each end
 A diamond is used as a decision symbol is used for branching
 A connector is often used on longer flowcharts
Looping will allow a program to do repetitive calculations
It is the ability of memory variables to change in value that makes computers and
programming worthwhile
Because one memory location can be used over and over again with different values, you
can write program instructions once and then use them for thousands of separate
calculations
Most languages allow both letters and digits within variable names
Different languages put different limits on the length of variable names
Newer languages tend to be case-sensitive
Most languages use camel casing where multiple words are run together with each new
word being capitalized
Variable naming rules (for this book)



Must be one word
Names should have some appropriate meaning
Variable names may not begin with a digit
All good computer questions have two mutually exclusive answers like yes or no or true
or false
Sentinel values represent an entry or exit point for a program
Programming languages can recognize the end of data in file automatically without using
a sentinel value through a code that is stored at the end of the data.
Connectors should contain a letter or number that can be matched with another location
Avoid using connectors whenever possible.
Most computer languages allow a shorthand expression for assignment statements that
give variables values
Whatever operation is performed to the right of the equal sign results in the value that is
placed in the memory location named to the left of the equal sign
It might help to imagine the word “let” in front of an assignment statement
It makes no sense to perform mathematical operations on memory locations, but it does
make sense to perform them on the contents of memory locations
Many programming languages allow you to create constants
Some languages require single quotes surrounding character constants while others
require double quotes.
Programmers must distinguish between numeric and character variables because
computers handle the two types of data differently, i.e. you cannot perform numeric
calculations on string data.
Finer distinctions may exist in some languages, such as those between integer and
floating-point variables
Literals are generally represented between quotation marks to distinguish them from
variable names
Summary
1) Together, hardware and software accomplish input, processing, output, and storage.
2) A programmer’s job involves understanding the problem, planning the logic, coding
the program, translating the program into machine language, testing the program and
putting the program into production
3) Data is stored in a hierarchy of characters, fields, records, and files
4) Pseudocode and flowcharts are used to plan logic
5) Variables are named memory locations. All variable names must be written as one
word without embedded spaces and should mean something
6) Testing a value means making a decision. All computer decisions include discreet
values
7) Most languages allow the equal sign to assign values to variables. Assignment always
takes place from right to left
8) Programmers must distinguish between numeric and character variables
Chapter Two: Understanding Structure
Objectives:
1)
2)
3)
4)
Understand what makes spaghetti code
Describe three basic structures making up structured programs
Understand primary reads
Recognize structure
Key terms:
Spaghetti Code: snarled program statements due to lack of structure
Unstructured code results in programs that may work, but are very difficult to read, with
logic that is difficult to follow
Understanding the Three Basic Structures
1) Sequence – performing an action and then the next action in order
2) Selection – ask a question and depending on the answer, you take one of two courses
of action. No matter which path you follow, you continue on with the next event.
3) Looping – you ask a question; if he answer requires an action, you perform the action
and ask the original question again. This continues until the answer to the questions is
such that the action is no longer required.
Any program, no matter how complicated, can be constructed using only three sets of
flowcharting shapes or structures; each basic unit of programming logic is a sequence, a
selection or a loop
Selection is called the if-then-else structure
A single alternative if structure also exists. The case where nothing is done on a branch is
called the null case.
Looping represents repetition or iteration.
The three basic structures can be combined in an infinite number of ways.
 Attaching structures end-to-end is called stacking
 Placing a structure within another structure is called nesting
Aligning steps vertically in pseudocode shows that they are “on the same level”
 Dependent steps are indented, showing they are “one level down”
In pseudocode, ENDIF always partners with the most recent IF
Each structure has only one entry and one exit point
Structured Programs
1) Includes only three types of structures
2) Structures connect to one another only at their entrance or exit points
3) With a sequence, each step must follow without any opportunity to branch away
a) Sequences never have decisions in them
4) With a selection, logic goes in one of two directions after the question; then the flow
comes back together
a) The question is not asked a second time
5) In a loop, if the question result in the procedure executing, then the logic returns to
the question that started the loop
a) The question is always asked again
b) The loop must go back directly to the question to be considered structured
i) The last step executed in the loop alters the condition tested in the question
that begins the loop, e.g. EOF
For a program to be structured and also work the way you want it to, sometimes you need
to add extra steps
1) The priming read (or priming input) is one kind of added step
a) Read in a separate statement
b) Purpose is to control the upcoming loop
Reasons for Structure
1)
2)
3)
4)
5)
Clarity
Professionalism
Efficiency
Maintenance
Modularity
When analyzing a flowchart, if a line is attached somewhere else, untangle it by repeating
the step that is tangled
Two Special Structures: Case and Do-Until
You can solve any logic problem with the sequencing, selection, and looping
Many languages allow two more structures:
1) Case structure
a) Test a variable against a series of values, taking appropriate action based upon the
variable’s value
b) Easier to read
c) A convenience, the computer still makes a series of individual decisions
2) Do-until
a) In a DO-WHILE, you may never enter the loop
b) A DO-UNTIL ensures that procedures execute at least once
c) You can create the same sequence generated by a DO-UNTIL loop by creating a
sequence followed by a DO-WHILE loop
Summary
1) Clearer programs can be constructed using sequences, selections and loops connected
in an infinite number of ways
a) Each structure has one entry and one exit point
2) A priming read is the step prior to beginning a structured loop
a) The last step in the loop gets the next and all subsequent input values
3) You can use a case structure when here are several distinct possible values for a
variable you are testing; the computer continues to treat them as individual decisions
4) A DO-UNTIL ensures that procedures execute at least once
Chapter Three: Modules, Hierarchy Charts and Documentation
Chapter Four: Writing a Complete Program
Chapter Five: Making Decisions
Chapter Six: Looping
Chapter Seven: Control Breaks
Chapter Eight: Arrays
Chapter Nine: Advanced Array Manipulation
Chapter Ten: Using Menus and Validating Input
Chapter Eleven: Sequential File Merging, Matching and Updating
Chapter Twelve: Advanced Modularization Techniques and
Object Oriented Programming
Chapter Thirteen: Programming Graphical User Interfaces
Chapter Fourteen: Program Design
Chapter Fifteen: System Modeling with UML
Appendix A: A Difficult Structuring Problem
Appendix B: Using a Large Decision Table
Index
Farrell, Joyce. “Programming Logic and Design”, Comprehensive Second Edition, Copyright 2002:
Course Technology, a division of Thompson Learning.
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