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Chapter 1 Basic Computer Concept

Chapter 1 Basic Computer Concept. 國立雲林科技大學 資訊工程研究所 張傳育 (Chuan-Yu Chang ) 博士 Office: ES 709 TEL: 05-5342601 ext. 4337 E-mail: chuanyu@yuntech.edu.tw. Textbook.

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Chapter 1 Basic Computer Concept

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  1. Chapter 1Basic Computer Concept 國立雲林科技大學 資訊工程研究所 張傳育(Chuan-Yu Chang ) 博士 Office: ES 709 TEL: 05-5342601 ext. 4337 E-mail: chuanyu@yuntech.edu.tw

  2. Textbook • G. Michael Schneider & Judith L. Gersting, “Invitation to Computer Science C++ Version”, 3rd Edition, 2004, ISBN:0-534-39097-8 • 台灣代理商：滄海書局 Tel：04-27088787Fax ：04-27087799

  3. A few Common Misconceptions about Computer Science • Misconception 1: • Computer science is the study of computers. • Many researchers investigate problems not with actual computers but rather with formal models of computation, which are easier to study and analyze mathematically. • Misconception 2: • Computer science is the study of how to write computer programs. • Programming is so primarily as a tool by which researchers can study new ideas and build and test new solutions. • Misconception 3: • Computer science is the study of the uses and applications of computers and software. • The computer scientist is responsible for specifying, designing, building, and testing software packages as well as the computer systems on which they run.

  4. The Definition of Computer Science • The central concept in computer science is the algorithm. [Gibbs and Tucker, 1986] • Computer science is the study of algorithms, including: • 1. Their formal and mathematical properties • 2. Their hardware realizations • 3. Their linguistic realizations • 4. Their applications

  5. The Definition of Computer Science (cont.) • Based on the definition, the tasks of the computer scientist are • Study the behavior of algorithms to determine whether they are correct and efficient. • Designing and building computer systems that are able to execute algorithms • Designing programming languages and translating algorithms into these languages so that they can be executed by the hardware. • Identifying important problems and designing correct and efficient software packages to solve these problems.

  6. The Definition the word Algorithm • Algorithm: • A procedure for solving a mathematical problem in a finite number of steps that frequently involves repetition of an operation; broadly: a step-by-step method for accomplishing some task. • An algorithm is an ordered sequence of instructions that is guaranteed to solve a specific problem. It looks like:Step 1 Do somethingStep 2 Do somethingStep 3 Do something : :Step N Stop, you are finished

  7. Three categories of operations • The operations used to construct algorithms can be categorized as • Sequential operations : • carries out a single well-defined task, usually expressed as simple declarative sentences. • Conditional operations : • “question-asking” instructions of an algorithm • Iterative operations : • “looping” instructions of an algorithm.

  8. Example:Algorithm for Programming the VCR • Step1 : • If the clock calendar are not correctly set, then go to page 9 of the instruction manual and follow the instructions there before proceeding. • Step2 : • Place a blank tape into the VCR tape slot. • Step3 : • Repeat step 4 through 7 for each program that you wish to record, up to maximum of 10 shows. • Step4 : • Enter the channel number that you wish to record, and press the button labeled CHAN.

  9. Algorithm for Programming the VCR (cont.) • Step5 : • Enter the time that you wish recording to start, and then press the button labeled TIME-START. • Step6 : • Enter the time that you wish recording to stop, and then press the button labeled TIME-FINISH. • Step7 : • This completes the programming of one show. If you do not wish to record anything else press the button labeled END-PROG. • Step8 : • Press the button labeled TIMER. Your VCR is now ready to record.

  10. Example:Algorithm for Adding Two m-digit Numbers • Given m >=1 and two positive numberseach containing m digits: am-1am-2 ……a0and bm-1bm-2……b0 • Wanted: cm-1cm-2…c0 where cm-1cm-2…c0 = (am-1am-2 ……a0 )+ (bm-1bm-2……b0)

  11. Example:Algorithm for Adding Two m-digit Numbers • Step 1: • Set the value ofcarry to 0 • Step 2: • Set the value of i equal to the value 0 • Step 3: • Repeat the instructions in steps 4 through 6 until the value of i is greater than m-1 • Step 4: • Add the two digits aiand bito the current value of carry to get ci • Step 5: • if ci>= 10 , reset cito (ci -10) and reset the value of carry to 1; otherwise, set the new value of carry to 0 • Step 6: • Add 1 to i , effectively moving one column to the left

  12. Algorithm for Adding Two m-digit Numbers (cont.) • Step 7: • set cm to the value of carry • Step 8: • print out the final answer, cmcm-1cm-2 … … … c0 • Step 9: • Stop

  13. Analyzing the algorithm • Steps 1,2,4,6,7,8,9: sequential operations • Step 5: conditional operations • Step 3: iterative operations

  14. Why formalizing the steps? • Why are formal algorithms so important in computer science ? • If we can specify an algorithm to solve a problem, then we can automate its solution. • The machine, robot, person , or thing carrying out the steps of the algorithm is called a computing agent. • Computer science can be viewed as “the science of algorithmic problem solving”. • Computability: is it true that every problem can be solved algorithmically? • Unsolvable problem • To specify an algorithm, but it would take a computing agent so long to execute that the solution is useless. • Ex. Chessboard: brute force algorithm • 假設在每一狀態有40個合法的移動，每盤棋約30步，則決定下第一步可有40x40x40x…x40=4030=1048 • 假設每秒可評估1012步，則須花3x1025年才能下哪一步。 • We do not yet know how to solve algorithmically. • Ex. intelligence

  15. The Formal definition of an Algorithm • The formal definition of an 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.

  16. Examples of algorithmsshampooing instructions • Step 1 Wet hair • Step 2 Lather • Step 3 Rinse • Step 4 Repeat

  17. Examples of algorithmsmaking a cherry pie • Step 1: Make the crust • 1.1 Take one and one-third cups flour • 1.2 Sift the flour • 1.3 Mix the sifted flour with one-half cup butter and one-fourth cup water. • 1.4 Roll into two 9-inch pie crusts. • Step 2: Make the cherry filling • 2.1 Open a 16-oz can of cherry pie filling and pour into bowl • 2.2 Add a dash of cinnamom and nutmeg, and stir. • Step 3: Pour the filling into the crust • Step 4: Bake at 350F for 45 minutes.

  18. Unambiguous • An unambiguous operation is one that can be understood and carried out directly by the computing agent without needing to be further simplified or explained. • An operation is unambiguous , we call it a primitive operation • It is not enough for an operation to be understandable. It must also be doable by the computing agent. • Doable means there exists a computational process that allows the computing agent to complete that operation successfully. • Effectively computable.

  19. Examples of algorithmsprime number • Step 1: Generate a list L of all the prime numbers: L1, L2, L3,… • Step 2: Sort the list L into ascending order. • Step 3: Print out the 100th element in the list L100. • Step 4: Stop Not doable

  20. Some examples of operations that may not be effectively computable: • Write out the exact decimal value p. • Set average to sum/number • Set the value of result to (N)1/2 • Add 1 to the current value of x

  21. …halts in a finite amount of time. • The result must be produced after the execution of a finite number of operations. • We must guarantee that the algorithm eventually reaches a statement that says “Stop, you are done”

  22. A correct solution to the Shampooing problem (1) • Step 1: Wet your hair. • Step 2: Set the value of WashCount to 0 • Step 3: Repeat step 4 through 6 until the value ofWashCount equals 2. • Step 4: Lather your hair • Step 5: Rinse your hair • Step 6: Add 1 to the value of WashCount • Step 7: Stop, you have finished shampooing your hair.

  23. A correct solution to the Shampooing problem (2) • Step 1: Wet your hair • Step 2: Lather your hair • Step 3: Rinse your hair • Step 4: Lather your hair • Step 5: Rinse your hair • Step 6: Stop, you have finished shampooing your hair.

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