1. Chapter 1 An Overview of Computers and Logic
An Object-Oriented Approach to Programming Logic and Design Second Edition
Chapter 1
An Overview of Computers and Logic

2. Objectives Learn about computer components and operations
Learn about the evolution of programming techniques
Learn about the steps involved in the programming process
Learn about flowcharts and pseudocode statements
An Object-Oriented Approach to Programming Logic and Design

3. Objectives (cont’d.) Create an application class with a main()method
Use and name variables
Assign values to variables
Describe data types
Learn about various forms of input
An Object-Oriented Approach to Programming Logic and Design

4. Understanding Computer Components and Operations
Two major computer system components
Hardware
Equipment or devices associated with the computer
Software
Programs (sets of instructions) written by programmers
Application software: applied to a task (word processing, spreadsheets, payroll, etc.)
System software: manages computer resources
An Object-Oriented Approach to Programming Logic and Design

5. Understanding Computer Components and Operations (cont’d.)
Four major hardware and software operations
Input
Processing
Output
Storage
Input operation
A means for data to enter computer through an input device
Mouse
Keyboard
An Object-Oriented Approach to Programming Logic and Design

6. Understanding Computer Components and Operations (cont’d.)
Processing data operation
Organizing
Checking for accuracy
Performing mathematical operations
Tasks occur in central processing unit (CPU)
Using machine instructions
Software
Provides machine instructions to CPU
Written using programming languages
An Object-Oriented Approach to Programming Logic and Design

7. Understanding Computer Components and Operations (cont’d.)
Output operation
A means to view, print, interpret, store data using output devices
Printer
Monitor
Hardcopy
Printed computer output
Softcopy
Screen output
An Object-Oriented Approach to Programming Logic and Design

8. Understanding Computer Components and Operations (cont’d.)
Storage operation
Storing output information on storage device hardware
Magnetic disks, compact discs, USB drives
Computer software
Instructions controlling data manipulation
Data input
Data processing
Data output or storage form
Gives hardware a purpose
An Object-Oriented Approach to Programming Logic and Design

9. Understanding Computer Components and Operations (cont’d.)
Obtaining programmer’s instructions (software)
Buying prewritten software stored on
Downloading software from the web
Write your own software instructions
Enter instructions through hardware devices
Store on storage device (disk, CD)
An Object-Oriented Approach to Programming Logic and Design

10. Understanding Computer Components and Operations (cont’d.)
Programming languages
Common languages
Visual Basic, C#, C++, COBOL, RPG, Fortran, JAVA
Programmers may specialize
Syntax
Rules governing usage and punctuation
Must be perfect
An Object-Oriented Approach to Programming Logic and Design

11. Understanding Computer Components and Operations (cont’d.)
Machine language
Circuitry consisting of millions of on-off switches
Computer’s on-off circuitry language
Compilers and interpreters
Language translation software
Identify correct/incorrect language use
Compilers
Create and store reusable machine instructions
Interpreters
Interpret programming language at run-time
An Object-Oriented Approach to Programming Logic and Design

12. Understanding Computer Components and Operations (cont’d.)
Two programming language errors
Syntax errors
Incorrect spelling
Incorrect structure of language elements
Semantic (logic) errors
Incorrect instructions
Incorrect order of instructions
Logic
Providing computer instructions in a specific sequence
An Object-Oriented Approach to Programming Logic and Design

13. Understanding Computer Components and Operations (cont’d.)
Logic (cont’d.)
Example: a logic error in cake-making instructions
Stir
Add two eggs
Add a gallon of gasoline
Bake at 350 degrees for 45 minutes
Add three cups of flour
Run or executed
Occurs after program written and compiled successfully
An Object-Oriented Approach to Programming Logic and Design

14. Understanding Computer Components and Operations (cont’d.)
Program instructions example
Written in English-like language
Three operations (input, processing, output)
Get inputNumber.
Compute calculatedAnswer as inputNumber times 2.
Print calculatedAnswer.
An Object-Oriented Approach to Programming Logic and Design

15. Understanding the Evolution of Programming Techniques
Storage categories
Internal and external needed by computer system
Internal storage
Memory, main memory, primary memory
Volatile main memory: lost when power turned off
Inside machine
Most often discussed in book
An Object-Oriented Approach to Programming Logic and Design

16. Understanding the Evolution of Programming Techniques (cont’d.)
Storage categories (cont’d.)
External storage
Persistent (relatively permanent) storage
Outside main memory (not necessarily outside computer)
Exists in devices
Disk drives: hard and floppy
Flash media
Magnetic tape
An Object-Oriented Approach to Programming Logic and Design

17. Understanding the Evolution of Programming Techniques (cont’d.)
Program execution
Program copy stored in main memory
Required data must be in memory location
Program calls location to obtain data
Processing occurs
Output displayed
An Object-Oriented Approach to Programming Logic and Design

18. Understanding the Evolution of Programming Techniques (cont’d.)
Modern computer programs
Around since 1940s
Oldest programming languages
Programmers worked with memory addresses
Memorized awkward codes associated with machine languages
Written as one piece
An Object-Oriented Approach to Programming Logic and Design

19. Understanding the Evolution of Programming Techniques (cont’d.)
Newer programming languages
Look like natural language
Easier to use
Reasons for ease of use
Use meaningful names for memory locations
No awkward memory addresses
Allow creation of self-contained modules or program segments
Can be pieced together
An Object-Oriented Approach to Programming Logic and Design

20. Understanding the Evolution of Programming Techniques (cont’d.)
Program development techniques
Procedural programming
Procedures created to manipulate data
Actions carried out (getting input data for an employee and writing the calculations)
Breaks process into manageable subtasks
An Object-Oriented Approach to Programming Logic and Design

21. Understanding the Evolution of Programming Techniques (cont’d.)
Program development techniques (cont’d.)
Object-Oriented programming (OOP)
Objects, attributes, behaviors, states
Attributes: object feature
Behaviors: what object does
States: set of all values of attributes
Describes objects’ features or attributes
An Object-Oriented Approach to Programming Logic and Design

22. Understanding the Evolution of Programming Techniques (cont’d.)
Program development techniques (cont’d.)
Differences
Programmer focus area in early stage
Object-oriented approach application types
Computer simulations
Create a model
Graphical user interfaces
Users interact with program in graphical environment
Natural use for object orientation
An Object-Oriented Approach to Programming Logic and Design

23. Understanding the Programming Process
Computer software system development
Three object-oriented approach tasks
Object-oriented analysis (OOA)
Analyzing the system
Object-oriented design (OOD)
Designing the system
Object-oriented programming (OOP)
Writing the programs
An Object-Oriented Approach to Programming Logic and Design

24. 1. Understanding the Problem
Programmer
Write programs to satisfy others needs
Provide services to users
First understand what users want
Well designed program
Steps might involve a short meeting
Poorly designed program
Steps might take many meeting hours
Thoroughly understanding problem
A most difficult aspect of programming
An Object-Oriented Approach to Programming Logic and Design

25. 2. Envisioning the Objects
Programmer
Envisions objects needed
Writes programming language instructions to create objects
Distinct steps
Data modeling
Identify all manipulated objects and relations
Create class
General object category
Establish communication means
Between objects, user
An Object-Oriented Approach to Programming Logic and Design

26. 3. Planning the Logic Heart of programming process Programmer
Plans program steps
Decides steps to include and order
Leads from available input to desired output
Plans the solution: two tools
Flowcharts and pseudocode
Both use English-like code
Language syntax not a concern
An Object-Oriented Approach to Programming Logic and Design

27. 3. Planning the Logic (cont’d.)
Think about all possible data values program might encounter
How to handle each scenario
Desk-checking
Walking through program’s logic on paper
Before writing the program
Focus of course
An Object-Oriented Approach to Programming Logic and Design

28. 4. Coding the Program Write class definitions
Descriptions data in each class
Operations performed with data in each class
Object-oriented languages
C++, C#, Java, Visual Basic, Smalltalk, OO COBOL, Simula
Similarity
All create objects and establishing communication
An Object-Oriented Approach to Programming Logic and Design

29. 4. Coding the Program (cont’d.)
Program object and logic needed to work with the objects
Executed using any number of languages
Syntax (correct spelling and punctuation )
Concern once language chosen
Experienced programmers
Combine planning and program coding in one step
An Object-Oriented Approach to Programming Logic and Design

30. 5. Translating the Program Code
Many programming languages
Computer knows one language
Its machine language consisting of many 1s and 0s
Translator programs (compilers or interpreters)
Change English-like high-level programming into low-level machine language
Executable program
Syntax error
Issues when translator cannot translate the code
Must be corrected to allow compilation to complete
An Object-Oriented Approach to Programming Logic and Design

31. 5. Translating the Program Code (cont’d.)
Figure 1-1 Creating an executable program.
An Object-Oriented Approach to Programming Logic and Design

32. 6. Testing the Program Syntax error free program
Not necessarily free of logical errors
Must test for logical errors
Requires entering of sample data
Select test data carefully
Error discovery may require changes
To program logic
To actual object design
Process resembles syntax error correction cycle
An Object-Oriented Approach to Programming Logic and Design

33. 7. Putting the Program into Production
Program adequately tested
Ready for organizational use
Putting program into production
Time to implement
Can be short or long
Depends on program nature, size and user needs
Factors
Training, data format changes, new platform causing users to make choices in unanticipated combinations
An Object-Oriented Approach to Programming Logic and Design

34. 7. Putting the Program into Production (cont’d.)
Non working program may cause significant monetary loss
Testing before deployment must be thorough
Conversion
Entire set of actions organization takes to switch over to new program (set of programs)
May take months or years to accomplish
An Object-Oriented Approach to Programming Logic and Design

35. 8. Maintaining the Program
Maintenance
Process of making required changes
Reasons
New legislated tax rates
Input file format alterations
End user requires additional information
Not included in original output specifications
An Object-Oriented Approach to Programming Logic and Design

36. 9. Retiring the Program Final programming process step
Program no longer needed by organization
New program in process of going into production
An Object-Oriented Approach to Programming Logic and Design

37. Using Flowcharts and Pseudocode Statements
Pictorial representation of logical program steps
Program steps in boxes
Connected with flowlines (arrows)
Shows processing order
Pseudocode
English-like representation of logical program steps
Looks like programming language (is not)
Important part of permanent documentation
Design and operation of software system
An Object-Oriented Approach to Programming Logic and Design

38. Using Flowcharts and Pseudocode Statements (cont’d.)
Figure 1-2 Flowchart of number-doubling problem
An Object-Oriented Approach to Programming Logic and Design

39. Creating an Application Class with a main() Method
Purely object-oriented programming languages
Every statement (application) part of class
“Pure View”
Application
Program accomplishing some task
Application pseudocode
Begins with word class
Ends with word endClass
No object-oriented programming language uses endClass
Used here for clarity
An Object-Oriented Approach to Programming Logic and Design

40. Creating an Application Class with a main() Method (cont’d.)
Set of statements performing task or group of tasks
Where program actions take place
If class contains one executable method
Method named main()
Identifier
Name of programming object
Class, method, or variable
An Object-Oriented Approach to Programming Logic and Design

41. Creating an Application Class with a main() Method (cont’d.)
Figure 1-3 Flowchart and pseudocode for main() method that prints “Hello”
An Object-Oriented Approach to Programming Logic and Design

42. Creating an Application Class with a main() Method (cont’d.)
Specific programming languages
Have rules for identifier structure
Book pseudocode rules
Identifier names
One word
Letters, digits, hyphens, underscores
No spaces
Identifiers should have appropriate meaning
Compound words allowed
Example: Helloclass
An Object-Oriented Approach to Programming Logic and Design

43. Creating an Application Class with a main() Method (cont’d.)
main() statement
Method header
Class containing main() method
An executable program
Every method ends with return statement
main() method action statements
Placed between main() method header and return statement
An Object-Oriented Approach to Programming Logic and Design

44. Creating an Application Class with a main() Method (cont’d.)
Figure 1-4 The Hello class written in the Java programming language
Figure 1-5 The Hello class written in the C# programming language
An Object-Oriented Approach to Programming Logic and Design

45. Using and Naming Variables
Variables (fields)
Memory locations
Contents can change over time
Holds just one value at any given time
Most objects in programs contain variables holding objects’ attributes
Same rules for naming variables as naming classes
An Object-Oriented Approach to Programming Logic and Design

46. Using and Naming Variables (cont’d.)
Table 1-1 Valid and invalid variable names for an employee’s last name
An Object-Oriented Approach to Programming Logic and Design

47. Assigning Values to Variables
Assignment statement
Statement assigning values to variables
Example: calculatedAnswer = inputNumber * 2
Assignment operator
Example: equal sign
Requires memory location name on left side where result stored
Named constant
Named memory location (similar to variable)
Value never changes during program execution
An Object-Oriented Approach to Programming Logic and Design

48. Assigning Values to Variables (cont’d.)
High-level computer language
Programmers pick reasonable “English” name for memory address
Computer keeps track of memory location
Mathematical operations
Performed on memory address contents
Operator precedence rules
Multiplication and division: precedence over addition and subtraction
Assignment operator has very low precedence
An Object-Oriented Approach to Programming Logic and Design

49. Understanding Data Types
Basic data types: text and numeric
Numeric constant (43)
Specific numeric value
Does not change
Digits with no quotation marks
Used for numeric calculations
String constant (“chris”)
Specific character set enclosed in double quotes
Character constant: single quotes (‘C’)
An Object-Oriented Approach to Programming Logic and Design

50. Understanding Data Types (cont’d.)
Two distinct variable types
Numeric variable
Holds a number
Character variables
Hold single character
String variables hold group of characters
Distinguish between numeric and character
Computers handle two data types differently
Language syntax rules define data type to expect
Done differently in every language
An Object-Oriented Approach to Programming Logic and Design

51. Understanding Data Types (cont’d.)
Variable declaration statement
Contains data type and identifier
Initializing a variable
Setting initial starting variable value
Popular languages (C++, C#, java, Visual Basic)
Distinguish integer (whole number) numeric variables and floating-point (fractional) numeric variables containing decimal point
Three broad types of variables
Numeric, character, string
An Object-Oriented Approach to Programming Logic and Design

52. Understanding Data Types (cont’d.)
Garbage value
Uninitialized variable containing unknown value
Default value
Automatic values for uninitialized variables
Text or character data handled differently from numeric data (every computer)
First step in writing programs
Identifying variables correctly
Numeric, character, string
Any programming language
An Object-Oriented Approach to Programming Logic and Design

53. Understanding Data Types (cont’d.)
Table 1-2 Some examples of legal and illegal assignments
An Object-Oriented Approach to Programming Logic and Design

54. Figure 1-6 Flowchart and pseudocode for the DoubleNumber class
An Object-Oriented Approach to Programming Logic and Design

55. Understanding Various Forms of Input
Simple programs require simple data
Data values often entered from keyboard
Users presented with a prompt
Message on monitor asking for user response
User interface
User’s means of interacting with the computer
Command prompt
Input area on computer screen
User can type text that communicates with computer’s operating system
An Object-Oriented Approach to Programming Logic and Design

56. Understanding Various Forms of Input (cont’d.)
Figure 1-7 A prompt followed by a response and output in a command-line environment
An Object-Oriented Approach to Programming Logic and Design

57. Understanding Various Forms of Input (cont’d.)
Figure 1-8 Flowchart and pseudocode for prompt and response in number-doubling program
An Object-Oriented Approach to Programming Logic and Design

58. Understanding Various Forms of Input (cont’d.)
Text environment
Many programs do not run at command prompt
Run using GUI
Typically contains graphical controls (buttons and text boxes)
User can manipulate with a mouse or other pointing device
An Object-Oriented Approach to Programming Logic and Design

59. Understanding Various Forms of Input (cont’d.)
Figure 1-9 A prompt, a response, and output in a GUI environment
An Object-Oriented Approach to Programming Logic and Design

60. Understanding Various Forms of Input (cont’d.)
Figure Flowchart and pseudocode for text box response in number-doubling program
An Object-Oriented Approach to Programming Logic and Design

61. Summary
Hardware and software accomplish four major operations: input, processing, output, and storage
Computer programming languages used to write machine instructions
Requires specific syntax
Procedural programming focuses on procedures programmers creates to manipulate data
OOP focuses on objects
Describes features or attributes and their behaviors
An Object-Oriented Approach to Programming Logic and Design

62. Summary (cont’d.) Programmer
Identifies objects and classes, codes program, translates into machine language, tests, puts into production
Flowcharts and/or pseudocode used to plan programming solution logic
Program actions occur within a method
Variables
Named memory locations, contents can vary
Choose meaningful variable names
An Object-Oriented Approach to Programming Logic and Design

63. Summary (cont’d.) Assignment always takes place from right to left
Variable declaration tells computer type of data to expect
Numeric, character, and string variables handled differently by computer
User input data
Text or graphical environment
File stored alone or in database
An Object-Oriented Approach to Programming Logic and Design