PROGRAMMING LOGIC AND DESIGN

FREFACE

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

1. An Overview of Computers and Logic

Objectives:

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

Hardware: equipment or devices associated with a computer
Software: instructions that tell the computer what to do

Major Operations

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

Memory
Main memory / primary memory

2) External storage

Floppy disk
Hard drive
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) Understand the problem

2) Plan the logic – developing an algorithm

3) Code the program

4) Translate the program into machine language

5) Test the program

6) Put the program into production

7) Maintaining a program

8) 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