1. Lecture 02: Problem Solving & Algorithms

3.  What is Problem Solving?  How to solve a problem?  Problem Solving Strategies  Solving problem with computer -Software Development Method of Problem Solving  Steps in the Software Development Method  Design & representation of algorithms  Programming errors & debugging  Program verification & testing  Program documentation

4.  Definition: ◦ Problem solving is the process of transforming the description of a problem into the solution of that problem by using our knowledge of the problem domain and by relying on our ability to select and use appropriate problem solving strategies, techniques and tools.

5.  Problem exist all around us  Can be as small as deciding where to have lunch.  Can be as big as saving a country’s faith.  But all problem can be solved!!  Problem solving is a knowledge building process.

6.  Step 1: Identify the problem  Step 2: Determine the problem solving strategy to apply  Step 3: Design the solution  Step 4: Execute the solution  Step 5: Evaluate the successfulness of the solution

7.  Many Strategies can be use in solving problem.  Most popular type of strategy is the “Art of War” by Sung Zhi (Ancient Chinese Philosopher)  We will learn: ◦ Guess and Check (Try an Error) ◦ Start at the end (Work Backward) ◦ Divide and Conquer ◦ Look for a Pattern

8.  Simplest strategy available.  Just experimenting with the possible solution.  A bit time consuming if have a lot of possible solution  But it is very efficient and practical for solving small or medium problem  Example Prince Carl divided 15 stone games into two piles: games he owns and games his brother owns. He owns 3 more games than his brother. How many games does his brother own?

9.  Solution ◦ I'll guess his brother owns 8 games. ◦ That means Prince Carl owns 11 games. That's a total of 19 games. ◦ My guess is too high. ◦ I'll guess again. This time I'll guess his brother owns 6 games. ◦ That means Prince Carl owns 9 games. That's a total of 15 games. ◦ My guess is right. ◦ His brother owns 6 games.

10.  Sometime to solve some problem, you may need to undo some of the key actions in the problem.  Also known as bottom-up approach  Example: The castle kitchen servants brought in 4 pies left over from the feast. 12 pies were eaten at the feast. Queen Mab took 2 home with her. How many pies did the servants bring into the feast at the beginning?

11.  Solution ◦ First, I'll account for all the pies that were eaten or taken home. ◦ 12 + 2 = 14 ◦ Then I'll add the 4 pies that were left over. ◦ 14 + 4 + 18 ◦ Therefore, there must have been 18 pies at the start of the feast.

12.  Most popular strategy used in problem solving.  Used by Napoleon in his quest to conquer the world.  We often break up large problems into smaller units that are easier to handle.

14.  More advance way to solve a complicated problem  Some problem can be solved by recognizing pattern within the domain.  For example: Daniel arranged loaves of bread on 6 shelves in the bakery. He put 1 loaf on the top shelf, 3 loaves on the second shelf, and 5 loaves on the third shelf. If he continues this pattern, how many loaves did Daniel put on the 6th shelf?

15.  Solution Shelf123456 Loave s 1357911

16.  Drawings/modeling  Logical Reasoning  Extra Information

17.  Computer can be programmed to do many complicated tasks at very high speeds and can store large quantities of information. Therefore, we can use computers as a tool in problem solving if one or more of the following conditions for a problem hold true: It has extensive input; It has extensive output; Its method of solution is too complicated to implement manually; If done manually, it takes an excessively long time to solve; We expect to use the same method of solution often in the future to solve the same problem with different inputs.

18.  Once using the computer, we need to write a program that consists of instructions corresponding to the steps of the solution such that the computer can interpret and execute them.  In developing the program, debugging it, expanding it in the future if necessary, and using it, we will have to remember certain details of the implementation. Consequently, the program has to be properly documented.

19.  Thus, we use software development method which consists of the following steps: Requirement specification Analysis Design Implementation Testing and verification Documentation

20. Steps to solve problemSoftware Development Method Step 1: Identify the problem Step 1: Requirement specification Step 2: Identify the possible solution and determine the best applicable solution Step 2: Analysis Step 3: Design the solution Step 3: Design Step 4: Execute the solution Step 4: Implementation Step 5: Evaluate the successfulness of the solution Step 5: Testing and verification Step 6: Documentation

21.  A documented step-by-step procedure in developing a program  Can operate under different models ◦ Waterfall ◦ Spiral Waterfall ◦ Agile Development ◦ Rapid Application Development

22.  Requirement Specification  Analysis  Design  Implementation & Deployment  Testing  Documentation

23.  A task to determine the needs and conditions (including scope) to meet in the new system  Requirements can be obtains through several methods ◦ Brainstorming session ◦ Survey ◦ Interview ◦ Observation ◦ others

24.  After obtaining the requirements, then the software developer need to study the approach/ method to solve the problem.  Using different problem techniques  Determine best solution from given options

25.  A crucial phase before the actual coding process  Several thing need to be consider during the design of a application or software ◦ Compatibility ◦ Extensibility ◦ Fault tolerance ◦ Reliability ◦ Reusability ◦ Robustness ◦ Usability

26.  Designing software usually is designing an Algorithm.  An Algorithm is a sequence of a finite number of steps arranged in a specific logical order, which, when executed, produce the solution for a problem.

27. An algorithm must satisfy some requirements : –Unambiguousness –It must not be ambiguous. In most cases we develop an algorithm so that it can be translated into program to be executed by computers. Computers cannot cope with ambiguous. Therefore, every step in an algorithm must be clear as to what it is supposed to do and how many times it is expected to be executed.

28. –Generality –It must have generality. A procedure that prints the message “One inch is 2.54 cm” is not an algorithm; however, one that converts a supplied number of inches to centimeters is an algorithm. –Correctness –It must be correct and must solve the problem for which it is designed. –Finiteness  It must execute its steps and terminate in finite time. An algorithm that never terminates is unacceptable.

29.  Usual tools in designing and documenting algorithms ◦ Pseudocode  a semiformal, English-like language (or other language that can be understand by human being) with a limited vocabulary that can be used to design and describe algorithms. ◦ Flowchart  a graph consisting of geometrical shapes that are connected by flow lines.

30.  A pseudocode can be used for: ◦Designing algorithms ◦Communicating algorithms to users ◦Implementing algorithms as programs ◦Debugging logic errors in program ◦Documenting programs for future maintenance and expansion purposes  To succeed in accomplishing its objectives, a pseudocode must meet these requirements: ◦Have a limited vocabulary ◦Be easy to learn ◦Produce simple, English-like narrative notation ◦Be capable of describing all algorithms, regardless of their complexity

31.  An algorithm can be written in pseudocode using six (6) basic computer operations:  A computer can receive information. Typical pseudocode instructions to receive information are: Read name Get name Read number1, number2 31

32.  A computer can output (print) information. Typical pseudocode instructions are: Print name Write "The average is", ave  A computer can perform arithmetic operation Typical pseudocode instructions: Add number to total Total = Total + Number Ave = sum/total 32

33.  A computer can assign a value to a piece of data: To assign/give data an initial value: Initialize total to zero Set count to 0 To assign a computed value: Total = Price + Tax 33

34.  A computer can compare two (2) pieces of information and select one of two alternative actions. Typical pseudocode e.g. If number < 0 then add 1 to neg_number else add one to positive number end-if 34

35.  A computer can repeat a group of actions. Typical pseudocode e.g. Repeat until total = 50 read number write number add 1 to total end-repeat OR while total < = 50 do: read number write number end-while 35

36. Start Read status if status is equal to 1 print “on” Else If status is equal to 0 print “ Off” else print “Error in status code” end_if end

37. Consider the following …. Problem: Baking a Cake How to solve: 1.Start 2.Preheat the oven at 180 o C 3.Prepare a baking pan 4.Beat butter with sugar 5.Mix them with flour, eggs and essence vanilla 6.Pour the dough into the baking pan 7.Put the pan into the oven 8.End

38. Problem: Prepare a Breakfast 1. Start 2. Prepare a Breakfast 3. End

39. 1. Start 2. Prepare a Breakfast 2.1. Prepare a tuna sandwich 2.1.1 Take 2 slices of bread 2.1.2 Prepare tuna paste 2.2. Prepare some chips 2.2.1 Cut potatoes into slices 2.2.2 Fry the potatoes 2.3. Make a cup of coffee 2.3.1 Boil water 2.3.2 Add water with sugar and coffee 3. End

40. What is the connection between these real life processes and algorithm? Something to ponder …

41. A specific and step-by-step set of instructions for carrying out a procedure or solving a problem, usually with the requirement that the procedure terminate at some point 2 types of algorithm representation will be explained: o Flowchart o Pseudocode

42.  Flowchart is another technique used in designing and representing algorithms.  It is an alternative to pseudocode; whereas a pseudocode description is verbal while a flowchart is graphical in nature.

43. Sub-module / Function (Barred Rectangle) Flow DirectionInput/Output ConnectorProcess DecisionStart/Stop RepresentationSymbolRepresentationSymbol

44. 44 This symbol shows where a program begins and ends (program or module). Labeling : When used to identify the beginning and end of a whole program, the beginning terminal is labeled with start and the ending terminal is labeled with end or stop. When the flowchart is for a module, the beginning terminal is labeled with the module name and the ending terminal is labeled with return or exit.

45. 45 Used to show tasks such as calculations, assignment statements, incrementing, etc. Labeling: Processes are labeled with the statement the task to be performed, for example: totalSales = subTotal + pstAmount + gstAmount Area = Length * Width firstName = "Sally" Area = Length * Width

46. 46 Used to show an operation that brings data into a program, or an operation that sends data out of the program. For example, getting values from the user or printing something on the screen. Labeling: Input/output symbols are labeled with the statement that receives the input or generates the output, which could also include opening files and devices. Examples: get stdNumber get stdNumber

47. 47 Used to identify a point in the program where a condition is evaluated. Conditions are used in if statements and looping. Labeling: Decisions are labeled with the condition that they are testing, for example: numRecords > 10 foundMatch = true numRecords > 10

48. 48 Used to connect two segments of flowchart that appear on the same page. This is done when your flowchart runs to the bottom of the page and you're out of room: end it with an on-page connector and then place another on-page connector in a free spot on the page, and continue the flowchart from that connector. Labeling: On-page connectors are labeled with upper-case letters. The connector at the end of a segment of flowchart will match the connector that identifies the rest of the flowchart. For example, when you run out of room, end the flowchart with a connector labeled "A". The flowchart continues at the matching connector also labeled "A".

49. 49 Used to specify a function/module call or a group of related statements. Example Start Submodule End Submodule Return

50. 50 A A A A

51. 51 Sequence structure statement_1 statement_2statement_n … Selection structure condition then-part else-part condition then-part Yes No ----------------------------------------------- --------------------

52. 52 Repetition structure conditi on loop-body Yes No

53. 53 The benefits of flowcharts are as follows: Communication Flowcharts are better way of communicating the logic of a system to all concerned. Effective analysis With the help of flowchart, problem can be analyzed in more effective way. Proper documentation Program flowcharts serve as a good program documentation, which is needed for various purposes. Efficient Coding The flowcharts act as a guide or blueprint during the systems analysis and program development phase. Proper Debugging The flowchart helps in debugging process. Efficient Program Maintenance The maintenance of operating program becomes easy with the help of flowchart. It helps the programmer to put efforts more efficiently on that part

54. Are the steps in the algorithm discussed earlier specific enough to be executed by computer? Something to ponder …

55. Input Process Output

56. Calculate and display the price of a number of apples if the quantity in kg and price per kg are given. Quantity Price_per_kg Price Price = Quantity * Price_per_kg Input Process Output

57. Input Quantity Start Price  Quantity * Price_per_kg Input Price_per_kg Output Price End

58. void main() { scanf(“%d”,&quantity); scanf(“%d”,&price_per_k g); price = quantity*price_per_kg; printf(“%d”, price); } It’s not complete! Declare the variables…

59.  In this phase, we implement the algorithm in a programming language.  During implementation we translate each step of the algorithm into a statement in that particular language and end up with a computer program. A computer program is a sequence of a finite number of statements expressed in a programming language in a specific logical order that, when executed, produce the solution for a problem.

60. 60 Programming Errors Another challenge that awaits is program debugging. Debugging is defined as the process of finding and correcting errors in computer programs. No matter how careful you are as a programmer, most programs you write will contain errors. Either they won’t compile or they won’t execute properly. This situation is something that happens very frequently to every programmer. You should take program debugging as a challenge, develop your debugging skills, and enjoy the process. There are three types of programming errors: Syntax errors Logic errors Run-time errors

61.  Syntax error: ◦ is violation of syntax rule, which define how the elements of a programming language must be written. ◦They occur during the implementation phase and are detected by the compiler during the compilation process. ◦Another name for syntax error is compilation error.  Logic error: ◦ occur during the analysis, design, and implementation phases. ◦We may choose an incorrect method of solution for the problem to be solved, mistakes in translating an algorithm into a program or design erroneous data for the program.  Run-time error: ◦Are detected by the computer while the program is being executed. ◦They are caused by program instructions that require the computer to do something illegal, such as attempting to store inappropriate data or divide a number by zero. ◦When a run-time error is encountered, the computer produces an error diagnostic message and terminates the program execution. 61

62.  To fix the program error, programmer will do debugging task by using debugger  Debugging process can be very frustrating especially involving huge amount of coding  Good to have good programming style and documentation in coding!

63.  Debugger ◦ is a computer program that is used to test and debug other programs. ◦ Usually comes together with compilers ◦ Debugger will help programmer by provide list of error in compiling the program ◦ Still depends on programmers to solve the problem!!

64.  Debugging technique ◦ Probe  Put an external variable inside the program and try to force the program to output result in the middle.  Good to trace modular logic error or data error ◦ Trace  Back-tracking or front-tracking  Go step-by-step (or line-by-line) to detect error.  Good in tracking logic error and

65. 65 In this phase, the main objective is to convince yourself and eventually your clients that the program will do what it is expected to do. In other words, you will want to verify that your program is correct. Program verification is the process of ensuring that a program meets user requirements. One of the techniques that can be used for program verification is program testing. Program testing is the process of executing a program to demonstrate its correctness. A program must be tested using a sufficiently large sample of carefully designed test data sets such that every logical path in the program is traversed at least once. You must continue to test your program until you are sure that all statements in it are functioning correctly.

66.  Program documentation consists of these elements: ◦A concise requirements specification ◦Descriptions of problem inputs, expected outputs, constraints, and applicable formula ◦A pseudocode and flowchart for its algorithm ◦A source program listing ◦A hardcopy of a sample test run of the program ◦A user’s guide explaining to non-programmer users how the program should be used.  Documentation can and should be done within the coding itself by using comments!! 66

67. Yes !! That’s all? What’s next??? INTRODUCTION TO C on the way …

68. 1.Design the algorithm for making a pot of tea

69. Pseudocode: Start Fill a kettle with water Boil the water in the kettle Put the tea leaves in the pot Pour boiling water in the pot End

70. Flowchart Start Fill a kettle with water Boil the water in the kettle Put the tea leaves in the pot Pour boiling water in the pot End

71. 2. Design the algorithm for calculating the perimeter of a circle

72. Pseudocode: Start Input Radius Calculate perimeter = 44/7 * Radius Print Perimeter End

73. Flowchart Start Perimeter = 44/7 * Radius Input Radius Print Perimeter End

74.  Any Questions?