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
Programming Logic and Design, Fifth Edition, Comprehensive

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
Programming Logic and Design, Fifth Edition, Comprehensive

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
Programming Logic and Design, Fifth Edition, Comprehensive

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
Programming Logic and Design, Fifth Edition, Comprehensive

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
Programming Logic and Design, Fifth Edition, Comprehensive

7. 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
Programming Logic and Design, Fifth Edition, Comprehensive

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
Programming Logic and Design, Fifth Edition, Comprehensive

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.
Programming Logic and Design, Fifth Edition, Comprehensive

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
Programming Logic and Design, Fifth Edition, Comprehensive

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
Programming Logic and Design, Fifth Edition, Comprehensive

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 user’s functional job tasks
Failure to understand the problem is the major cause of most project failures
Programming Logic and Design, Fifth Edition, Comprehensive

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
Programming Logic and Design, Fifth Edition, Comprehensive

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
Programming Logic and Design, Fifth Edition, Comprehensive

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
Programming Logic and Design, Fifth Edition, Comprehensive

16. Figure 1-1 Creating an executable program
Using Software to Translate the Program into Machine Language (continued)
Figure 1-1 Creating an executable program
Programming Logic and Design, Fifth Edition, Comprehensive

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
Programming Logic and Design, Fifth Edition, Comprehensive

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)
Programming Logic and Design, Fifth Edition, Comprehensive

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
Programming Logic and Design, Fifth Edition, Comprehensive

20. Understanding Interactive User Input (continued)
Figure 1-2 A prompt, response, and output in a command line environment
Programming Logic and Design, Fifth Edition, Comprehensive

21. Understanding Interactive User Input (continued)
Figure 1-3 A prompt, response, and output in a GUI environment
Programming Logic and Design, Fifth Edition, Comprehensive

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
Programming Logic and Design, Fifth Edition, Comprehensive

23. Understanding the Data Hierarchy and File Input (continued)
Figure 1-4 The data hierarchy
Programming Logic and Design, Fifth Edition, Comprehensive

24. Understanding the Data Hierarchy and File Input (continued)
Figure 1-5 The EMPLOYEE file represented as a stack of index cards
Programming Logic and Design, Fifth Edition, Comprehensive

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
Programming Logic and Design, Fifth Edition, Comprehensive

26. Using Flowchart Symbols and Pseudocode Statements (continued)
Figure 1-6 Input symbol
Programming Logic and Design, Fifth Edition, Comprehensive

27. Using Flowchart Symbols and Pseudocode Statements (continued)
Figure 1-7 Processing symbol
Programming Logic and Design, Fifth Edition, Comprehensive

28. Using Flowchart Symbols and Pseudocode Statements (continued)
Figure 1-8 Output symbol
Programming Logic and Design, Fifth Edition, Comprehensive

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
Programming Logic and Design, Fifth Edition, Comprehensive

30. Using Flowchart Symbols and Pseudocode Statements (continued)
Figure 1-9 Flowchart and pseudocode of program that doubles a number
Programming Logic and Design, Fifth Edition, Comprehensive

31. Using Flowchart Symbols and Pseudocode Statements (continued)
Figure Inefficient pseudocode for program that doubles 10,000 numbers
Programming Logic and Design, Fifth Edition, Comprehensive

32. Using Flowchart Symbols and Pseudocode Statements (continued)
Figure Flowchart of infinite number-doubling program
Programming Logic and Design, Fifth Edition, Comprehensive

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
Programming Logic and Design, Fifth Edition, Comprehensive

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 employee’s last name
Programming Logic and Design, Fifth Edition, Comprehensive

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
Programming Logic and Design, Fifth Edition, Comprehensive

36. Ending a Program by Using Sentinel Values (continued)
Figure Flowchart of number-doubling program with sentinel value of 0
Programming Logic and Design, Fifth Edition, Comprehensive

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
Programming Logic and Design, Fifth Edition, Comprehensive

38. Ending a Program by Using Sentinel Values (continued)
Figure Flowchart using eof
Programming Logic and Design, Fifth Edition, Comprehensive

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
Programming Logic and Design, Fifth Edition, Comprehensive

40. Managing Large Flowcharts (continued)
Figure Flowchart using the connector
Programming Logic and Design, Fifth Edition, Comprehensive

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
Programming Logic and Design, Fifth Edition, Comprehensive

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
Programming Logic and Design, Fifth Edition, Comprehensive

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
Programming Logic and Design, Fifth Edition, Comprehensive

44. Understanding Data Types (continued)
Table 1-2 Some examples of legal and illegal assignments
Programming Logic and Design, Fifth Edition, Comprehensive

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
Programming Logic and Design, Fifth Edition, Comprehensive

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
Programming Logic and Design, Fifth Edition, Comprehensive

47. Summary Four major computer operations: Six programming phases: 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
Programming Logic and Design, Fifth Edition, Comprehensive

48. Summary (continued) Data hierarchy:
Character
Field
Record
File
Database
Flowchart: pictorial representation of program logic
Variables: named memory locations that contain values
Programming Logic and Design, Fifth Edition, Comprehensive

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
Programming Logic and Design, Fifth Edition, Comprehensive

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
Programming Logic and Design, Fifth Edition, Comprehensive