1. Chapter 1: An Introduction to Computer Science Invitation to Computer Science, Java Version, Third Edition

2. Invitation to Computer Science, C++ Version, Fourth Edition 2 Objectives In this chapter, you will learn about The definition of computer science Algorithms

3. Invitation to Computer Science, C++ Version, Fourth Edition 3 Introduction Common misconceptions about computer science  Computer science is the study of computers  Computer science is the study of how to write computer programs  Computer science is the study of the uses and applications of computers and software

4. Invitation to Computer Science, C++ Version, Fourth Edition 4 The Definition of Computer Science Gibbs and Tucker definition of computer science  Computer science is the study of algorithms that is used to solve problems.  The problem solving process involves 4 steps: Creating correct and efficient algorithms Building computers to execute algorithms Designing programming languages to translate algorithms Applications

5. Invitation to Computer Science, C++ Version, Fourth Edition 5 Quiz 1. (T/F) Computer science is the study of allergy. 2. (T/F) Building cars is one of problems solving steps used by computer scientists. 3. (T/F) Designing programming languages is the third step of problems solving steps used by computer scientists.

6. Invitation to Computer Science, C++ Version, Fourth Edition 6 The Definition of Computer Science (continued) Algorithm  An ordered step by step instructions that is guaranteed to solve a specific problem

7. Invitation to Computer Science, C++ Version, Fourth Edition 7 The Definition of Computer Science (continued) An algorithm is a list that looks like  STEP 1: Do something.  STEP 2: Do something.  STEP 3: Do something. ..  STEP N: Stop. You are finished.

8. Invitation to Computer Science, C++ Version, Fourth Edition 8 Example of Algorithm: How to make sticky rice? 1. Measure Your Sticky Rice. 2. Add Water and Let Soak. 3. Add Salt and Bring to a Boil. 4. Cook the Rice. 5. Use a Fork to Check the Rice. 6. Allow Rice to Steam-Cook for 20 min.. 7. Enjoy Your Sticky Rice!

9. Invitation to Computer Science, C++ Version, Fourth Edition 9 Criteria for Correct Algorithm Criteria  1. unambiguous instructions  2. computable instructions  3. producing results  4. stopping in a finite amount of time Example: 1. Add X to some numbers ->violate criteria 1 2. Set X to (5 / 0) ->violate criteria 2 and 3 3. Repeat Step 4 Until X > 10 ->violate criteria 4 4. Set X = 1 5. Stop

10. Invitation to Computer Science, C++ Version, Fourth Edition 10 Algorithm Operation 1: Sequential Operation Sequential operations  Carry out a single well-defined task; when that task is finished, the algorithm moves on to the next operation Examples:  1. Set X to 1  2. Set Y to 2  3. Set Z to X + Y  4. Print Z  5. Stop

11. Invitation to Computer Science, C++ Version, Fourth Edition 11 Quiz What is the output of Step 4 of the following algorithm? 1. Set Y to 4 2. Set W to 2 3. Set P to (Y + W) / 2 4. Print P 5. Stop

12. Invitation to Computer Science, C++ Version, Fourth Edition 12 Quiz What is the output of Step 4 of the following algorithm? 1. Set Y to 4 2. Set W to Y + 2 3. Set Y to (Y + W) / 2 4. Print Y 5. Stop

13. Invitation to Computer Science, C++ Version, Fourth Edition 13 Algorithm Operation 1: Conditional Operation  Conditional operations Ask a question and then select the next operation to be executed on the basis of the answer to that question Examples  1. Set X to 1  2. If X is even then Set Y to 1 else Set Y to 2  3. Stop

14. Invitation to Computer Science, C++ Version, Fourth Edition 14 Quiz What is the output of Step 3 of the following algorithm?  1. Set X to 4  2. If X > 3 then Set Y to ‘A’ else Set Y to ‘B’  3. Print Y  4. Stop

15. Invitation to Computer Science, C++ Version, Fourth Edition 15 The Definition of Computer Science (continued)  Iterative operations Go back and repeat the execution of a previous block of instructions Examples  1. Set X to 1  2. Repeat Step3 Until X is 3  3. Set X to X + 1  4. Stop

16. Invitation to Computer Science, C++ Version, Fourth Edition 16 Quiz What is the output of Step 3 of the following algorithm?  1. Set X to 1  2. Set Y to 2  3. Repeat Step4-5 Until X is 3  4. Set X to X + 1  5. Set Y to Y + 2  6. Stop

17. Invitation to Computer Science, C++ Version, Fourth Edition 17 What is the output of Step 6 of the following algorithm?_____ How many times have step 4 been executed? ____  1. Set X to 1  2. Set Y to 2  3. Repeat Step4-5 Until X is Y > 7  4. Set X to X + 3  5. Set Y to Y + 3  6. Print Y  7. Stop

18. Invitation to Computer Science, C++ Version, Fourth Edition 18 Quiz What is the output of Step 6 of the following algorithm?_____ How many times have step 4 been executed? ____  1. Set X to 1  2. Set Y to 2  3. Repeat Step4-5 Until X is Y > 7  4. Set X to X + 3  5. Set Y to Y + 3  6. Print X  7. Stop

19. Invitation to Computer Science, C++ Version, Fourth Edition 19 What is boolean? a boolean is either TRUE or FALSE What is the output of the following algorithm?___ 1. Set B to FALSE 2. If B is TRUE then Set A to ‘OK’ else Set A to ‘YES’ 3. Print A 4. Stop

20. Invitation to Computer Science, C++ Version, Fourth Edition 20 Quiz What is the output of step 4 of the following algorithm?___ Has the statement ‘Set A to TRUE’ been executed? _____ 1. Set B to TRUE 2. If B is TRUE then Set A to FALSE Else Set A to TRUE 3. If A is FALSE then Set W to ‘X’ Else Set W to ‘Y’ 4. Print W 5. Stop

21. Invitation to Computer Science, C++ Version, Fourth Edition 21 What is the output on step 6? ________ How many times of step 4 been executed? _______ 1. Set INDEX to 0 2. Set DONE to false 3. Repeat steps 4-5 until DONE is true 4. Set INDEX to INDEX + 1 5. If INDEX > 2 then Set DONE to true 6. Print INDEX 7. Stop

22. Invitation to Computer Science, C++ Version, Fourth Edition 22 Quiz What is the output on step 6? ________ How many times of step 4 been executed? _______ 1. Set INDEX to 1 2. Set DONE to false 3. Repeat steps 4-5 until DONE is true 4. Set INDEX to INDEX + 2 5. If INDEX > 5 then Set DONE to true 6. Print INDEX 7. Stop

23. Invitation to Computer Science, C++ Version, Fourth Edition 23 Repeat/Until Repeat A Until B meaning if B is not true then do A.

24. Invitation to Computer Science, C++ Version, Fourth Edition 24 While /Do While A Do B  meaning if A is true then do B

25. Invitation to Computer Science, C++ Version, Fourth Edition 25 What is the output of step 6?_____ How many times have step5 been executed? ____ 1. Set INDEX to 1 2. Set SUM to 1 3. While INDEX <= 5 do steps 4 - 5 4. Set SUM to SUM + INDEX 5. Set INDEX to INDEX + 2 6. Print SUM 7. Stop

26. Invitation to Computer Science, C++ Version, Fourth Edition 26 Quiz What is the output of step 6?_____ How many times have step5 been executed? ____ 1. Set INDEX to 2 2. Set SUM to 3 3. While INDEX <= 8 do steps 4 - 5 4. Set SUM to SUM + INDEX 5. Set INDEX to INDEX + 3 6. Print SUM 7. Stop

27. Invitation to Computer Science, C++ Version, Fourth Edition 27 What is the output of step 8?_____ How many times have step5 been executed? ____ 1. Set INDEX to 1 2. Set SUM to 1 3. Set DONE to false 4. While DONE is false do steps 5-7 5. Set SUM to SUM + INDEX 6. Set INDEX to INDEX + 3 7. If INDEX > 7 THEN Set DONE to true 8. Print SUM 9. Stop

28. Invitation to Computer Science, C++ Version, Fourth Edition 28 Quiz What is the output of step 8?_____ How many times have step5 been executed? ____ 1. Set INDEX to 1 2. Set SUM to 1 3. Set DONE to false 4. While DONE is false do steps 5-7 5. Set SUM to SUM + INDEX 6. Set INDEX to INDEX + 3 7. If INDEX > 7 THEN Set DONE to true 8. Print SUM 9. Stop

29. Invitation to Computer Science, C++ Version, Fourth Edition 29 Quiz - Challenge What is the output on step 6? ________ How many times of step 4 been executed? _______ 1. Set INDEX to 0 2. Set DONE to true 3. Repeat steps 4-5 until DONE is true 4. Set INDEX to INDEX + 1 5. If INDEX > 2 then Set DONE to true 6. Print INDEX 7. Stop

30. Invitation to Computer Science, C++ Version, Fourth Edition 30 Quiz What is the output of step 8?_____ How many times have step5 been executed? ____ 1. Set INDEX to 1 2. Set SUM to 1 3. Set DONE to true 4. While DONE is false do steps 5-7 5. Set SUM to SUM + INDEX 6. Set INDEX to INDEX + 3 7. If INDEX > 7 THEN Set DONE to true 8. Print SUM 9. Stop

31. Invitation to Computer Science, C++ Version, Fourth Edition 31 Chapter 1. Exercises Samples Exercise 5.  Under what conditions would the following function not be effectively computable? F(x) = sqrt(a)/b

32. Invitation to Computer Science, C++ Version, Fourth Edition 32 Chapter 1. Exercises Samples Exercise 7. What is the output of the following algorithm if X is 5 and Y is 2? 1. Get X 2. Get Y 3. Divide X by Y and call the reminder R 4. If R is not 0 then reset X to X-1 and go back to step 3. 5. Print X 6. Stop

33. Invitation to Computer Science, C++ Version, Fourth Edition 33 Exercise 9 Samples Write an algorithm to compute the area of a rectangle. Area = Length * Width 1. Get Length 2. Get Width 3. Set Area = Length * Width 4. Print Area 5. Stop

34. Invitation to Computer Science, C++ Version, Fourth Edition 34 Quiz Write an algorithm to compute the area of a triangle. Rule: Area = Height * Width / 2

35. Invitation to Computer Science, C++ Version, Fourth Edition 35 Exercise 9 Sample. Write an algorithm to determine the financial status. Rule: If the savings > $10000 then output ‘Good’ otherwise ‘Bad’. 1. Get Savings 2. If Savings > $10000 Set Status = “Good” Else Set Status = “Bad” 3. Print Status 4. Stop

36. Invitation to Computer Science, C++ Version, Fourth Edition 36 Quiz Write an algorithm to determine the weather status. Rule: If the temperature < 32F then output ‘Cold’ otherwise ‘Warm’.

37. Invitation to Computer Science, C++ Version, Fourth Edition 37 Quiz Write an algorithm to compute the following mysterious equation. Be sure to print the error message when C is 0. rule: A = B / C

38. Invitation to Computer Science, C++ Version, Fourth Edition 38 Example. If/else Write an algorithm to compute and display the value sqrt(x) if the value of x is not negative. If x is negative, then display the message ‘Unable to perform the sqrt() operation.’ 1. Get X 2. If X < 0  Print “Unable to perform the sqrt()”  Else  Print sqrt(x) 3. Stop

39. Invitation to Computer Science, C++ Version, Fourth Edition 39 Quiz Write an algorithm to compute and display the value a/b if the value of b is not 0. If b is 0, then display the message ‘Unable to perform the division.’

40. Invitation to Computer Science, C++ Version, Fourth Edition 40 Loop Exercise 1. The worst solution. Write an algorithm to compute Sum = 2+3+4? 1. Set Sum to 0 2. Set Num to 2 3. Set Sum = Sum + Num 4. Set Num to Num + 1 5. Set Sum = Sum + Num 6. Set Num to Num + 1 7. Set Sum = Sum + Num 8. Print Sum 9. Stop

41. Invitation to Computer Science, C++ Version, Fourth Edition 41 Loop Exercise 2. The best solution Write an algorithm to compute Sum = 2+3+4? 1. Set Sum to 0 2. Set Count to 1 3. Set Num to 2 4. While Count <=3 Do Steps 5-7 5. Sum = Sum + Num 6. Num = Num + 1 7. Count = Count + 1 8. Print Sum 9. Stop

42. Invitation to Computer Science, C++ Version, Fourth Edition 42 Loop Exercise 2. The best solution Write an algorithm to compute Sum = 2+3+4? 1. Set Sum to 0 2. Set Count to 1 3. Set Num to 2 4. Repeat Sept 5-7 Until Count > 3 Do 5. Sum = Sum + Num 6. Num = Num + 1 7. Count = Count + 1 8. Print Sum 9. Stop

43. Invitation to Computer Science, C++ Version, Fourth Edition 43 Quiz. Loop. Use While/Do to write an algorithm to compute  sum = 1 + 2 + 3 + 4+ 5 + 6 + 7 + 8 + 9 + 10

44. Invitation to Computer Science, C++ Version, Fourth Edition 44 Quiz. Loop. Use Repeat/Until to write an algorithm to compute  sum = 1 + 2 + 3 + 4+ 5 + 6 + 7 + 8 + 9 + 10

45. Invitation to Computer Science, C++ Version, Fourth Edition 45 Use While/Do to write an algorithm to compute  sum = 2 + 4 + 6 + 8 + 10

46. Invitation to Computer Science, C++ Version, Fourth Edition 46 The Definition of Computer Science (continued)  Iterative operations Tell us to go back and repeat the execution of a previous block of instructions Examples  Repeat the previous two operations until the mixture has thickened  While there are still more checks to be processed, do the following five steps  Repeat steps 1, 2, and 3 until the value of y is equal to 11

47. Invitation to Computer Science, C++ Version, Fourth Edition 47 The Definition of Computer Science (continued) If we can specify an algorithm to solve a problem, we can automate its solution Computing agent:  The machine, robot, person, or thing carrying out the steps of the algorithm  Does not need to understand the concepts or ideas underlying the solution

48. Invitation to Computer Science, C++ Version, Fourth Edition 48 The Formal Definition of an Algorithm Algorithm  A well-ordered collection of unambiguous and effectively computable operations that, when executed, produces a result and halts in a finite amount of time Unambiguous operation  An operation that can be understood and carried out directly by the computing agent without needing to be further simplified or explained  Ambiguous example, ‘Set X to some number’

49. Invitation to Computer Science, C++ Version, Fourth Edition 49 The Formal Definition of an Algorithm (continued) A primitive operation (or a primitive) of the computing agent  Operation that is unambiguous for computing agent  Primitive operations of different individuals (or machines) vary  An algorithm must be composed entirely of primitives Effectively computable  Computational process exists that allows computing agent to complete that operation successfully  Ineffectively computable example, ‘Generate a list of prime numbers’

50. Invitation to Computer Science, C++ Version, Fourth Edition 50 The Formal Definition of an Algorithm (continued) The result of the algorithm must be produced after the execution of a finite number of operations  Infinite loop The algorithm has no provisions to terminate A common error in the designing of algorithms Infinite loop example,  Step 1. Wet the car  Step 2. Repeat Step 3  Step 3. Wash the car

51. Invitation to Computer Science, C++ Version, Fourth Edition 51 The Importance of Algorithmic Problem Solving Algorithmic solutions can be:  Encoded into some appropriate language  Given to a computing agent to execute The computing agent  Would mechanically follow these instructions and successfully complete the task specified  Would not have to understand Creative processes that went into discovery of solution Principles and concepts that underlie the problem

52. Invitation to Computer Science, C++ Version, Fourth Edition 52 The Early Period: Up to 1940 3,000 years ago: Mathematics, logic, and numerical computation  Important contributions made by the Greeks, Egyptians, Babylonians, Indians, Chinese, and Persians 1614: Logarithms  Invented by John Napier to simplify difficult mathematical computations Around 1622: First slide rule created

53. Invitation to Computer Science, C++ Version, Fourth Edition 53 The Early Period: Up to 1940 (continued) 1672: The Pascaline  Designed and built by Blaise Pascal  One of the first mechanical calculators  Could do addition and subtraction 1674: Leibnitz’s Wheel  Constructed by Gottfried Leibnitz  Mechanical calculator  Could do addition, subtraction, multiplication, and division

54. Invitation to Computer Science, C++ Version, Fourth Edition 54 Figure 1.4 The Pascaline: One of the Earliest Mechanical Calculators

55. Invitation to Computer Science, C++ Version, Fourth Edition 55 The Early Period: Up to 1940 (continued) 1801: The Jacquard loom  Developed by Joseph Jacquard  Automated loom  Used punched cards to create desired pattern 1823: The Difference Engine  Developed by Charles Babbage  Did addition, subtraction, multiplication, and division to 6 significant digits  Solved polynomial equations and other complex mathematical problems

56. Invitation to Computer Science, C++ Version, Fourth Edition 56 The Early Period: Up to 1940 (continued) 1823: The Difference Engine  Developed by Charles Babbage  Capabilities: Addition, subtraction, multiplication, and division to 6 significant digits Solve polynomial equations and other complex mathematical problems

57. Invitation to Computer Science, C++ Version, Fourth Edition 57 Figure 1.5 Drawing of the Jacquard Loom

58. Invitation to Computer Science, C++ Version, Fourth Edition 58 The Early Period: Up to 1940 (continued) 1830s: The Analytic Engine  Designed by Charles Babbage  More powerful and general-purpose computational machine  Components were functionally similar to the four major components of today’s computers Mill (modern terminology: arithmetic/logic unit) Store (modern terminology: memory) Operator (modern terminology: processor) Output (modern terminology: input/output)

59. Invitation to Computer Science, C++ Version, Fourth Edition 59 The Early Period: Up to 1940 (continued) 1890: U.S. census carried out with programmable card processing machines  Built by Herman Hollerith  These machines could automatically read, tally, and sort data entered on punched cards

60. Invitation to Computer Science, C++ Version, Fourth Edition 60 The Birth of Computers: 1940–1950 Development of electronic, general-purpose computers  Did not begin until after 1940  Was fueled in large part by needs of World War II Early computers  Mark I  ENIAC  ABC system  Colossus  Z1

61. Invitation to Computer Science, C++ Version, Fourth Edition 61 Figure 1.6 Photograph of the ENIAC Computer

62. Invitation to Computer Science, C++ Version, Fourth Edition 62 The Birth of Computers: 1940–1950 Stored program computer model  Proposed by John Von Neumann in 1946  Stored binary algorithm in the computer’s memory along with the data  Is known as the Von Neumann architecture  Modern computers remain, fundamentally, Von Neumann machines  First stored program computers EDVAC EDSAC

63. Invitation to Computer Science, C++ Version, Fourth Edition 63 The Modern Era: 1950 to the Present First generation of computing (1950-1959)  Used vacuum tubes to store data and programs  Each computer was multiple rooms in size  Computers were not very reliable

64. Invitation to Computer Science, C++ Version, Fourth Edition 64 The Modern Era: 1950 to the Present (continued) Second generation of computing (1959-1965)  Replaced vacuum tubes by transistors and magnetic cores  Dramatic reduction in size Computer could fit into a single room  Increase in reliability of computers  Reduced costs of computers  High-level programming languages The programmer occupation was born

65. Invitation to Computer Science, C++ Version, Fourth Edition 65 The Modern Era: 1950 to the Present (continued) Third generation of computing (1965-1975)  Used integrated circuits rather than individual electronic components  Further reduction in size and cost of computers Computers became desk-sized First minicomputer developed  Software industry formed

66. Invitation to Computer Science, C++ Version, Fourth Edition 66 The Modern Era: 1950 to the Present (continued) Fourth generation of computing (1975-1985)  Reduced to the size of a typewriter  First microcomputer developed  Desktop and personal computers common  Appearance of Computer networks Electronic mail User-friendly systems (Graphical user interfaces) Embedded systems

67. Invitation to Computer Science, C++ Version, Fourth Edition 67 Figure 1.7 The Altair 8800, the World’s First Microcomputer

68. Invitation to Computer Science, C++ Version, Fourth Edition 68 The Modern Era: 1950 to the Present (continued) Fifth generation of computing (1985-?)  Recent developments Massively parallel processors Handheld devices and other types of personal digital assistants (PDAs) High-resolution graphics Powerful multimedia user interfaces incorporating sound, voice recognition, touch, photography, video, and television

69. Invitation to Computer Science, C++ Version, Fourth Edition 69 The Modern Era: 1950 to the Present (continued) Recent developments (continued)  Integrated global telecommunications incorporating data, television, telephone, FAX, the Internet, and the World Wide Web  Wireless data communications  Massive storage devices  Ubiquitous computing

70. Invitation to Computer Science, C++ Version, Fourth Edition 70 Figure 1.8 Some of the Major Advancements in Computing

71. Invitation to Computer Science, C++ Version, Fourth Edition 71 Figure 1.8 Some of the Major Advancements in Computing

72. Invitation to Computer Science, C++ Version, Fourth Edition 72 Organization of the Text This book is divided into six separate sections called levels Each level addresses one aspect of the definition of computer science Computer science/Algorithms

73. Invitation to Computer Science, C++ Version, Fourth Edition 73 Organization of the Text Level 1: The Algorithmic Foundations of Computer Science  Chapters 1, 2, 3 Level 2: The Hardware World  Chapters 4, 5 Level 3: The Virtual Machine  Chapters 6, 7

74. Invitation to Computer Science, C++ Version, Fourth Edition 74 Organization of the Text Level 4: The Software World  Chapters 8, 9, 10, 11 Level 5: Applications  Chapters 12, 13, 14 Level 6: Social Issues  Chapter 15

75. Invitation to Computer Science, C++ Version, Fourth Edition 75 Figure 1.9 Organization of the Text into a Six-Layer Hierarchy

76. Invitation to Computer Science, C++ Version, Fourth Edition 76 Summary Computer science is the study of algorithms An algorithm is a well-ordered collection of unambiguous and effectively computable operations that, when executed, produces a result and halts in a finite amount of time If we can specify an algorithm to solve a problem, then we can automate its solution Computers developed from mechanical calculating devices to modern electronic marvels of miniaturization