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Turgay Korkmaz Office: NPB 3.330 Phone: (210) 458-7346 Fax: (210) 458-4437

CS xxxx Foundations of Programming and Data Structures Ch 0 – Overview Problem Solving using Computing Systems. Turgay Korkmaz Office: NPB 3.330 Phone: (210) 458-7346 Fax: (210) 458-4437 e-mail: korkmaz@cs.utsa.edu web: www.cs.utsa.edu/~korkmaz.

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Turgay Korkmaz Office: NPB 3.330 Phone: (210) 458-7346 Fax: (210) 458-4437

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  1. CS xxxx Foundations of Programming and Data Structures Ch 0 – Overview Problem Solving using Computing Systems Turgay Korkmaz Office: NPB 3.330 Phone: (210) 458-7346 Fax: (210) 458-4437 e-mail: korkmaz@cs.utsa.edu web: www.cs.utsa.edu/~korkmaz

  2. Think Like a Programmer: Introduction https://www.youtube.com/watch?v=YgzpqlF54lo&list=PLcr1-V2ySv4TiAm4cqzS3corkJl_QCl5H Problem Solving using generic or ad hoc methods in an orderly manner to find solutions to problems [wiki]. • In CS, problem solving requires to • develop algorithms and data structures • Algorithms: • Figure out necessary instructions/steps • Data structures: • Figure out how to organize data in a computer • Coding of the algorithm and the data structure in a programming language (we will use C)

  3. Problem Solving • Can computers think or develop a solution? • No! You do! • Computers just follow your instructions and do them faster! • Then how do computers do many things? Even play chess! • Is it possible for different programmers/students to get the same solution for a given problem? • Depends on the problem. If simple, yes. But in general, no! • We may come up with different but yet correct solutions. • Efficiency vs. Cost

  4. Computing System is a system that includes the computing unit (CPU) and memory along with peripherals (I/O devices). Internal Memory CPU Processor Control Unit I/O Devices ALU • Main memory stores both data and instructions (how?) • Control unit contains a program counter (PC) showing the address of the next instruction to execute (e.g., +-*/, compare, jump). I/O devices von Neumann Architecture: store and computation

  5. * How is the information stored in Memory? CPU • Bits, bytes • Memory is a sequence of bytes (8-bit info, char in C) • Every byte is identified by a numeric address • Values larger than a byte (char) are stored in consecutive bytes • Suppose we declare char ch = ‘A’; int x = 305; Suppose we have 4MB memory

  6. Memory Organization CPU

  7. How a CPU Works https://www.youtube.com/watch?v=cNN_tTXABUA How does a simple CPU work? CPU PC = 4 Instruction Reg= R1= R2= R3= R4= R5= int A, B=2, C=3, D=5; A=B+C+D; Compiler/linker (gcc) Machine executable file containing code and data

  8. Speed of CPU (GHz) Size of Memory (Gbyte) 8 bits = 1 bytes Word = 4 bytes How many bytes does this computer have? 32 bytes = 25 How many bytes you have if it says 2Gbyte? 1K=210 = 1024 1M=220 = 10242 1G=230 = 10243 When referring to a computer processor or CPU, GHz is a clock frequency, also known as a clock rate or clock speed, representing a cycle of time. An oscillator circuit supplies a small amount of electricity to a crystal each second that is measured in kHz, MHz, or GHz. "Hz" is an abbreviation of Hertz, "k" represents Kilo (thousand), "M" represents Mega (million), "G" represents Giga (thousand million). [computerhope.com] 1K=103 1M=106 1G=109

  9. Internal Memory Computing System I/O Devices • How does a program (code + data) get into main memory? • Who gets it from Hard Disk to Main (internal) Memory? • Who stored it on Hard Disk in the first place? • Operating System (kernel) • And other system programs CPU Processor Control Unit ALU software

  10. What is an Operating System (OS)? . • User View • User interface, ease of use vs. performance (windows vs. command line; terminal vs. minicomputer; networked workstations; handheld; embedded ) • System View • OS is a resource allocator • Manages all resources (CPU, memory, file-storage, I/O devices etc.) • Decides between conflicting requests for efficient and fair resource use • OS is a control program • Controls execution of programs to prevent errors and improper use of the computer • Users • People, machines, other computers • Application programs • Word processors, compilers, web browsers, database systems, video games • Operating system • An intermediary between users/applications and the computerhardware • Hardware • CPU, memory, I/O devices

  11. Computer Software • Operating System - Provides an interface with the user • unix, windows, linux, ... • Software Tools • word processors (MS Word, WordPerfect, ...) • spreadsheet programs (Excel, Lotus1-2-3, ...) • mathematical computation tools (MATLAB, Mathematica, ...) • Computer Languages • machine language • assembly language • binary language • high level languages (C, C++, Ada, Fortran, Basic, java) • WE WILL STUDY C PROGRAMMING LANGUAGE on Linux abstractions

  12. What is C? • General purpose, machine-independent, high-level programming language • Developed at Bell Labs in 1972 by Dennis Ritchie • American National Standards Institute (ANSI) approved ANSI C standard in 1989 Source file

  13. Hello World! in Linux • Login to a Linux machine • SSH Secure Shell (e.g., elk03.cs.utsa.edu) elk03 :> mkdirmyprog elk03 :> cdmyprog elk03 :> picohello.c • Type your program … and save it (ctrl-o) • Compile and execute your program elk03 :> gcchello.c –o hello elk03 :> hello

  14. Think Like a Programmer: Introduction https://www.youtube.com/watch?v=YgzpqlF54lo&list=PLcr1-V2ySv4TiAm4cqzS3corkJl_QCl5H PROBLEM SOLVING Very Important If you can develop solution, then coding in C is easy… So, before studying C, let us C a few examples of problem solving

  15. Re-call computing system! * Input CPU Processor Control Unit Internal Memory ALU In this sense, do you think humans are like a computer? + we have intelligence and we can solve problems and develop algorithms while computers just follow our instructions… When developing algorithms, it may help to act like a computer! I/O Devices External Memory Output

  16. Problem Solving Methodology • 1. State the problem clearly • 2. Describe the input/output information • 3. Work the problem by hand, give example • 4. Develop a solution • (Design Algorithms + Data Structures) and • Convert them to a program (C program) • 5. Test the solution with a variety of data

  17. (x1,y1) (x2, y2) Example 1 1. Problem statement Compute the distance between two points 2. Input/output description straight line in a plane Point 1 (x1, y1) Distance between two points (distance) Point 2 (x2, y2)

  18. Example 1 (cont’d) 3. Hand example side1 = 4 - 1 = 3 side2 = 7 - 5 = 2

  19. Example 1 (cont’d) 4. Algorithm development and coding a. Generalize the hand solution and list/outline the necessary operations step-by-step • Give specific values for point1 (x1, y1) and point2 (x2, y2) • Compute side1=x2-x1 and side2=y2-y1 • Compute • Print distance b. Convert the above outlined solution to a program using any language you want (see next slide for C imp.)

  20. Example 1 (cont’d)

  21. Example 1 (cont’d) 5. Testing • After compiling your program, run it and see if it gives the correct result. • Your program should print out The distance between two points is 3.61 • If not, what will you do?

  22. x1=2, y1=5, x2=10, y2=8, Modification to Example 1 How will you find the distance between two other points (2,5) and (10,8)?

  23. Simple examples to develop solutions

  24. x=3 cm y=4 cm x y area Compute the area of a triangle • State problem • I/O • Hand example • Develop solution and Coding • Testing area = ½ * 3 *4 = 6 cm2 • Get values of x and y • Compute area = ½*x*y • Print area

  25. H total_sec M S Given the number of seconds, find number of hours, minutes and seconds • State problem • I/O • Hand example • Develop solution and Coding • Testing 3675 seconds can be written as 1 hour 1 min 15 sec • Get total_sec • H = total_sec / 3600 (integer division) • M = (total_sec – (H*3600)) / 60 • M = (total_sec mod 3600) / 60 • S = total_sec – (H*3600) – (M*60) • Print H hour, M min, S sec

  26. A little bit difficult examples to develop solutions Sequence of instructions, Selections, Loops Some problems are from How to Solve it: Modern Heuristics by Michalewicz and Fogel. Springer 2004.

  27. Income, grade, speed Average speed • Suppose a car goes from city A to city B with speed of 40 mph and immediately comes back with the speed of 60 mph. • What is the average speed? • Can you generalize this solution and outline step by step to find average speed when the speed from A to B is X and the speed from B to A is Y? Sequence of Instructions

  28. Average speed

  29. no yes Assign a letter grade • Suppose I have your grades as follows final midterm avg_hwquizze letter 30 20 30 4 ? How can I determine your letter grade? Sequence of Instructions and Selection of Instructions

  30. no yes no yes Assign letter grades to whole class? • Suppose I have your grades as follows name final midterm avg_hwquizze letter aaaa 30 20 30 4 ? bbbb 20 15 40 10 ? … How to assign letter grade to each? Sequence Selection Repletion

  31. Think Like a Programmer: Introduction https://www.youtube.com/watch?v=YgzpqlF54lo&list=PLcr1-V2ySv4TiAm4cqzS3corkJl_QCl5H More examples

  32. OPT Dimensions of a rectangle ranch? • A farmer has a rectangular ranch with a perimeter of P=110 meters and an area of A=200 square meters. • What are the dimensions of his ranch? • What are the dimensions for any P and A? y x

  33. no yes no yes Climbing a wooden post • A snail is climbing a wooden post that is H=10 meters high. • During the day, it climbs U=5 meters up. • During the night, it falls asleep and slides down D=4 meters. • How many days will it take the snail to climb the top of the post? • Given that H > U > D. Can you generalize your solution for any H, U, and D?

  34. Self-study Minimum number of coins • Suppose you want to give x=67 cents to a person, what is the minimum number of coins • You have many 25, 10, 5, 1 cents

  35. no yes no yes Example: Sum of numbers Given n (for example n=1000), compute • sum = 1+2+3+…+n • sum_odd =1+3+5+7+…+(2n+1) • ln2=1- 1/2 + 1/3 - 1/4 +…  1/n

  36. Ten heuristics for problem solving How to Solve it: Modern Heuristics by Michalewicz and Fogel. Springer 2004. • Don’t rush to give an answer, think about it • Concentrate on the essentials and don’t worry about the noise (tiny details) • Sometimes finding a solution can be really easy (common sense), don’t make it harder on yourself • Beware of obvious solutions. They might be wrong • Don’t be misled by previous experience

  37. Ten heuristics for problem solving How to Solve it: Modern Heuristics by Michalewicz and Fogel. Springer 2004. • Start solving. Don’t say “I don’t know how” • Most people don’t plan to fail, they just fail to plan! • Don’t limit yourself to the search space that is defined by the problem. Expand your horizon • Constraints can be helpful to focus on the problem at the hand • Don’t be satisfied with finding asolution, look for better ones • Be patient. Be persistent!

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