High-level software (Ch.9) Algorithms and data structures. Low-level software. Components Circuits Gates Transistors

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1 High-level software (Ch.9) Algorithms and data structures Low-level software Components Circuits Gates Transistors

2 Remember: Decision-making instructions BR Set PC to operand unconditionally BRLT i Set PC to operand if A < 0 BREQ i Set PC to operand if A = 0 2

3 Flowcharts! We use decision-making instructions to build: branches loops 3

4 6.5 Algorithms and Pseudocode Algorithm = A sequence of steps for solving a problem Muḥammad ibn Mūsā al-khwārizmī ( A.D.) 4

5 Not in text How to describe an algorithm in an intuitive way? Flowcharts! 5

6 Not in text Problems with flowcharts: They re hard to follow when they get complex 6

7 Problems with flowcharts: They re hard to draw in electronic documents Not in text 7

8 Problems with flowcharts: They re hard to draw in electronic documents Not in text Our text uses only pseudocode 8

9 6.5 Algorithms and Pseudocode Pseudocode = A mixture of English and formatting to make the steps in an algorithm explicit There are no syntax rules in pseudocode! Pseudocode is not case sensitive! Example: Repeated-division algorithm (convert base-10 number to other bases): While ( the quotient is not zero ) Divide the decimal number by the new base Make the remainder the next digit to the left in the answer Replace the original decimal number with the quotient 9

10 Algorithms can also be described in natural language! 10

11 but pseudocode is more precise IF concerned about cholesterol Put butter substitute in a pot ELSE Put butter in a pot Turn on burner Put pot on the burner WHILE (NOT bubbling) Leave pot on the burner Put other ingredients in the blender Turn on blender WHILE (more in pot) Pour contents into lender in slow steam Turn off blender 11

12 Pseudocode functionality Pseudocode has all of the concepts encountered in any high-level programming language, only the syntax is informal: Variables Assignment I/O Selection / decision Repetition / loop Boolean expressions 12

13 To do for next time Read pp of the text, referring to your Python experience 13

14 We can test a pseudocode algorithm w/pencil & paper, a.k.a. desk checking While ( the quotient is not zero ) Divide the decimal number by the new base Make the remainder the next digit to the left in the answer Replace the original decimal number with What is 93 in base 8? 93/8 gives 11 remainder 5 11/6 gives 1 remainder 3 1/ 8 gives 0 remainder 1 answer

15 Organizing the solution in a computer-like way gives us better idea of what is required for the computer to execute it, e.g. two numbers need to be entered, etc. 15

16 Pseudocode for Complete Computer Solution (in Python) Write "Enter the new base" Read newbase Write "Enter the number to be converted" Read decimalnumber Set quotient to 1 WHILE (quotient is not zero) Set quotient to decimalnumber DIV newbase Set remainder to decimalnumber REM newbase Make the remainder the next digit to the left in the answer Set decimalnumber to quotient Write "The answer is " Write answer 16

17 How to Develop an Algorithm in Pseudocode Problem: Read in pairs of positive numbers and print each pair in order. First version: WHILE (not done) Write "Enter two values separated by blanks" Read number1 Read number2 Print them in order Do you see any problems with this algorithm? 17

18 WHILE (not done) Write "Enter two values separated by blanks" Read number1 Read number2 Print them in order In order to be able to write a computer program to implement this algorithm, several extra questions need to be settled. We say that the algorithm is not concrete yet. 18

19 Pseudocode Refining the algorithm How do we know when we re done? Let the user tell us how many Where do we store the user s response? In a variable. Let s call it numberofpairs How do we keep track of how many pairs have been entered? With another variable! Let s call it numberread How do we print the numbers in order? If first number is smaller print first, then second If first number if larger 19 print second, then first

20 Second version: Write "How many pairs of values are to be entered?" Read numberofpairs Set numberread to 0 WHILE (numberread < numberofpairs) Write "Enter two values separated by a blank; press return" Read number1 Read number2 IF(number1 < number2) Print number1, " ", number2 ELSE Print number2," ", number1 Make numberread equal to itself plus 1 20 Is it concrete yet?

21 Desk checking Data Fill in values during each iteration 3 numberread number1 number numberofpairs What is the output? 21

22 Translating Pseudocode into a Computer Program What kind of program? Machine language Nooooooo! Assembly language Very detailed and time consuming, but sometimes it needs to be done High-level language Python! 22

23 SKIP 6.6 Testing 23

24 Read and take notes in notebook: Software Piracy and Copyrighting Have you every "borrowed" software from a friend? Have you ever "lent" software to a friend? Did you know that about 100,000 jobs are lost in the US every year due to such "borrowing" and "lending?" 24

25 Chapter Review Questions List the operations that a computer can perform Describe the important features of the Pep/8 virtual machine Distinguish between immediate addressing mode and direct addressing mode Write a simple machine-language program Distinguish between machine language and assembly language 25

26 Chapter Review Questions Describe the steps in creating and running an assembly-language program Write a simple program in assembly program Distinguish between instructions to the assembler (a.k.a. directives) and instructions to be translated into machine code (a.k.a. executable instructions) Distinguish between following an algorithm and developing one 26

27 Chapter Review Questions Describe the pseudocode constructs used in expressing an algorithm Use pseudocode to express and algorithm 27

28 Second homework for ch.6 44, 45 28

Low-level software. Components Circuits Gates Transistors

Low-level software. Components Circuits Gates Transistors QUIZ Pipelining A computer pipeline has 4 processors, as shown above. Each processor takes 15 ms to execute, and each instruction must go sequentially through all 4 processors. A program has 10 instructions.