CARIBBEAN EXAMINATIONS COUNCIL

1. CARIBBEAN EXAMINATIONS COUNCIL CARIBBEAN SECONDARY EDUCATION CERTIFICATE (CSEC) INFORMATION TECHNOLOGY SYLLABUS TEACHER ORIENTATION WORKSHOP AUGUST 11TH – 15TH, 2008 TRINIDAD & TOBAGO Facilitator: Gerard Phillip

2. PROBLEM–SOLVINGCSEC INFORMATION TECHNOLOGY

3. INTRODUCTION • How are instructions given to the computer? • Computer programs – finite set of precise instructions written in a computer language • Before program is written we must find a way to solve the problem • After figuring out how to solve the problem we then translate the solution into a language meaningful to the computer

4. INTRODUCTION • Giving precise, unambiguous instructions is not inherent in human nature • Consider the following: Proceed a mile or so down the road until you reach the roundabout. Turn left at the roundabout and follow the road until you reach a green house on the right hand side. The Post office is about the 3rd or 4th building on the right after the green house. You can’t miss it!

5. INTRODUCTION • Problem-solving statements/ instructions should be: • Precise • Unambiguous • Must be in a logical sequence • Finite, i.e. terminate after a definite number of steps • Teachers must ensure that students have a good grasp of what these attributes mean • Students should engage students in problem-solving exercises involving everyday problems they can relate to.

6. PROBLEM-SOLVING ON THE COMPUTER • Examples of everyday problems: • Write a recipe for making a cheese sandwich • Write instructions to teach your mom how to retrieve voice message from a generic cell phone • Write instructions to give directions to a visitor to get to the nearest hospital, starting from the school premises • Write instructions to tell a novice how to download music from the Internet.

7. PROBLEM-SOLVING ON THE COMPUTER • The design of any computer program involves two phases: • The Problem-solving Phase • The Implementation Phase • Problem-Solving Phase comprises the following steps: • Define the problem • Analyse the problem • Propose and Evaluate possible solutions • Select the most efficient solution and represent it as an algorithm • Test and validate the algorithm for correctness • Implement the Algorithm • Run the Program • Document and maintain the program

8. DEFINING THE PROBLEM • The problem must first be defined: Ensure that students understand the Problem • Defining the problem is the first step towards finding a solution • It helps the programmer to understand what is given and what is required • If the programmer does not fully understand what is required, he/she cannot produce the desired solution to the problem

9. DEFINING THE PROBLEM • One of the biggest challenges faced in problem-solving is understanding the problem to be solved. • Defining the program can be accomplished by decomposing the problem into three key components: • What is given (the inputs) • The tasks that must be performed (processing) • The expected results (the output)

10. THE DEFINING DIAGRAM • Define the problem by constructing a defining diagram • A table with three columns which represents the three components: input, processing and output. • E.g. A program is required to read three numbers and calculate and print the total.

11. THE DEFINING DIAGRAM • Input refers to the source data provided - easily identified by the keywords – given, read or accept, input • Output refers to the end result required - keywords are print, display, produce, output • Processing are the actions that must be performed to achieve the required output - it answers the question: What must I do with the inputs in order to produce the desired result?

12. THE DEFINING DIAGRAM • In the defining diagram, the actions must be listed in a logical sequential manner • All necessary actions must be explicitly stated • The processing section is NOT the solution to the problem. It’s simply the actions that must be done in order to solve the problem • Note that in some cases the input, processing and output statements might not be as explicitly stated.

13. PROBLEM 2 • E.g. of problem not clearly stated to facilitate student identification of the problem: Given three integers representing the age of three boys respectively, write a solution to find their average age and also determine the age of the oldest boy. • This problem statement could have been stated more precisely to read: Given three integers A, B, C, representing the age of three boys respectively, write a solution to find and display their average age as well as the age of the eldest boy.

14. DEFINING DIAGRAM • Two major tasks to be performed, each consisting of multiple actions:

15. PROBLEM 3 The cost of a new car is the sum of the wholesale cost, the local sales tax and the dealer’s percentage mark-up. Assuming that the dealer’s mark-up is 10 percent of the wholesale cost and the sales tax is 6 percent, design an algorithm to read a car ID (an integer value) and the wholesale cost of the car (a real value) and print the car ID and the cost to the consumer.

16. PROBLEM 3 • Here, input and output data are clearly stated. To determine the processing steps we may ask “What should I do with wholesale cost in order to find the cost to the consumer?”

17. THE PROBLEM WITH PROBLEM SPECIFICATION • Many real-world programming problems are not always precise • Initial descriptions are often vague, and ambiguous • Students should be encouraged to evaluate problem statements and ask questions if they are perceived as ambiguous • Also, some information may be implicit in the problem statement and therefore should be taken into account when defining the problem

18. THE PROBLEM WITH PROBLEM SPECIFICATION Have students evaluate several problem statements, ranging from simple to complex, some precise, some ambiguous, lacking pertinent information. Here are some examples of imprecise problem statements: • #4: Write a program to print a list of all the employees who have been in the company for over five years • #5: Write a program that reads a file that contains information on the height, weight and age of 100 children. The program should print the names of all the children who are overweight.

19. FINDING A SOLUTION TO THE PROBLEM • Introduction • The Concept of Variables • Choosing Variable Names • Initialization of Variables

20. FINDING A SOLUTION TO THE PROBLEMINTRODUCTION Now that we have defined the problem, we know what we need to do. We must now figure out how to do it. • A problem can have many different solutions • Let students arrive at one that works, however long-winded • Once a solution is found, it can then be reviewed to see how it can be optimized, or made more efficient • The first approach in deriving a solution to a problem is to do the problem by hand, noting each step as you proceed.

21. FINDING A SOLUTION TO THE PROBLEMINTRODUCTION Problem #6:Find and print the average of three numbers • Define the problem • Create sample data: sample input data 5, 3, 25 • Execute each processing step in the defining diagram manually

22. FINDING A SOLUTION TO THE PROBLEMINTRODUCTION • Having completed a manual solution to the problem, the next step is to write your solution as a sequence of instructions • Initial solution • Get the first number, call it num1 • Get the second number, call it num2 • Get the third number, call it num3 • Add num1 + num2 + num3 • Divide result by 3 • Print result • Stop

23. FINDING A SOLUTION TO THE PROBLEMTHE CONCEPT OF VARIABLES In our solution to problem #6, we did not tell the computer where to put the result of the add operation. The result must be stored somewhere so it can be accessed later. Grandma’s fluffy pancakes: Method: Sift flour in mixing bowl ... Melt the butter in a frying pan ... Pour batter into a bowl ... Just as we need containers to hold or store ingredients, likewise, in computation, we need something to store or hold the values we manipulate

24. FINDING A SOLUTION TO THE PROBLEMTHE CONCEPT OF VARIABLES • In the computer, values are stored in memory locations. • There are many memory locations, so in order to keep track of where our values are stored we need to place a label or identifier on a particular memory location. • The label or identifier is called a variable. • A variable is a symbolic name assigned to a memory location that stores a particular value

25. FINDING A SOLUTION TO THE PROBLEMTHE CONCEPT OF VARIABLES • When we say num1, num2, etc we are actually defining a variable or an identifier for each number, so that we can refer to (access) it later. • We need to tell the computer where to put the result of the addition of num1, num2, num3 • Add num1 + num2 + num3 storing in Sum • This would tell the computer that the result of the computation should be stored in a memory location called Sum.

26. FINDING A SOLUTION TO THE PROBLEMTHE CONCEPT OF VARIABLES Likewise, we must address a similar issue in the last two statements where we stated, Divide result by 3 Print result • Computations are performed by the ALU, part of the CPU and results are temporarily stored in registers within the cpu • These values must be stored in memory locations if they are to be accessed later

27. THE CONCEPT OF VARIABLES • The word variable is derived from the verb ‘to vary’. This means that the value stored in a particular location can change from time to time, although the label remains the same. • When new values are placed into previously assigned memory locations, the old values are replaced by the new .

28. FINDING A SOLUTION TO THE PROBLEMTHE CONCEPT OF VARIABLES • It is always useful to illustrate the concept of a variable by using diagrams to show the memory locations: Memory locations Num 1 Variables Num 2 Num 3

29. FINDING A SOLUTION TO THE PROBLEMTHE CONCEPT OF VARIABLES We can now revise the initial solution to include the new variables called sum and average Get three numbers, say num1, num2, num3 Add num1, num2, num3, storing in sum Divide sum by 3, storing in average Print average

30. THE CONCEPT OF VARIABLESCHOOSING VARIABLE NAMES • It’s good practice to choose variable names that reflect the kind of data that is being stored • It helps the programmer as well as the reader to understand the solution better • It’s important that students grasp the concept of variables very early in the problem-solving phase.

31. EVALUATE ALTERNATIVE SOLUTIONS • Having found a solution to a problem the programmer should proceed to explore alternative solutions • The aim is to arrive at the most efficient solution • The initial solution is usually the first that comes to mind, but is not always the best solution • The programmer must evaluate all feasible alternatives and choose the optimal solution

32. EVALUATE ALTERNATIVE SOLUTIONS Points to consider when developing alternative solutions. • Can the result be derived differently? • Can the solution be made more general? Would it work if there were 100 integers, instead of 3? • Can the solution be used for another problem? E.g. Average temperature or average grade? • Can the number of steps be reduced and still maintain the logic? Can it be made more robust? What would happen if incorrect data is entered?

33. REDUCING THE NUMBER OF STATEMENTS We can reduce the number of statements by combining two arithmetic statements into one: • Add num1, num2, num3 can be written as Sum = num1 + num2 + num3 (the variable sum is assigned the value of num1 plus num2 plus num3) • Divide sum by 3 storing in average can be written Average = sum/3 We can combine the two statements to produce: Average = sum/3

34. REVISED SOLUTION Option 1 Get num1, num2, num3 Sum = num1 + num2 + num3 Average = sum/3 Print Average Stop Option 2 Get num1, num2, num3 Average = (num1 + num2 num3)/3 Print Average Stop • The most efficient solution should have the following attributes: • Should be maintainable • Should be memory efficient • Should be robust

35. INITIALIZATION OF VARIABLES • Variables that are used as counters or used to store totals should always be assigned an initial value of 0 before they are incremented. • This is called initialization • E.g. Count = 0 • This ensures that the variable is cleared of any values that may have been assigned in a previous execution of the program.

36. WHAT IS AN ALGORITHM? At this time, we can now introduce the term ‘algorithm’. An algorithm is a sequence of precise instructions for solving a problem in a finite number of steps. Properties: • Algorithms must: • be precise, • be unambiguous, • be logically sequenced, • give the correct solution an all cases, and • eventually end.

37. WHAT IS AN ALGORITHM? Algorithmic structure Header : Algorithm’s name or title Declaration : Brief description of algorithm and variables used. i.e. A statement of purpose as well as the initialization of variables Body : Sequence of steps Terminator : An end statement

38. ALGORITHMIC STRUCTURE Problem: Write an algorithm that prompts a student to enter his/her name and age, accepts the name and age and then display a welcoming message on the screen such as “hello Michael! You are 16 years old!” Write the algorithm identifying the header, declaration, body and terminator.

39. ALGORITHMIC STRUCTURE Algorithm Student data {Header} This algorithm displays a student’s name and age on the screen. {declaration} Start Display “Enter your name:” Accept Name Display “Enter your age:” Accept Age Display “Hello”, Name Display “You are”, Age, “years old” Stop {Terminator} {Body}

40. FLOWCHARTS VERSUS PSEUDOCODE • Pseudocode is more concise, closely resembles programming language • Flowchart gives good view of the structure and flow of the logic • Beginners tend to follow the logic easier when using flowcharts rather than pseudocode • Longer, more complex solutions are better represented using pseudocode.

41. FLOWCHARTS VERSUS PSEUDOCODE • Usage is a matter of preference for experienced programmers • Students should be asked to use both flowcharts as well as pseudocode to represent algorithms • Flowcharts must use special geometrical objects that designate the basic steps of a program: Processing/ Assignment Start/ Stop Input/Output Decision

42. PSEUDOCODE AND FLOWCHART Start • Start • Get num1, num2, num3 • Average (num1 + num2 + num3)/3 • Print Average • Stop Read num1, num2, num3 Average (num1+num2+num3)/3 Print Average Stop

43. SELECTION STRUCTURES Selection (decision) The IF…THEN selection statement Syntax: IF (expression) THEN {Statement (s)} Execute this statement if logical expression is TRUE This construct is used when no action needs to be performed if the expression returns false.

44. SELECTION STRUCTURES Get Mark IF Mark >= 50 THEN Print “Well done” Stop This requires only that the expression “Well done” be printed should the student score 50 marks or more. No action is intended should the mark be less than 50

45. SELECTION STRUCTURES • IF … THEN … ELSE construct syntax: • IF (expression) THEN {Statements} executed only if condition is TRUE ELSE {Statements} executed only if condition is FALSE ENDIF • Only one group of statements could be executed each time the program is executed.

46. SELECTION STRUCTURES Get Mark IF Mark >= 50 THEN PRINT “ Well done” ELSE PRINT “Must do better” ENDIF Stop • “Well done” will be printed should the student’s mark be 50 or greater. • If the mark is less than 50 then the statement “Must do better” would be printed.

47. SELECTION STRUCTURES A worker in a clothing factory is paid an additional incentive according to the amount of shirts she folds. The basic salary is $300.00 per week. Should the worker fold 500 or more shirts per week, an additional 15%, is added to her basic salary. If the worker folds less than 500 shirts however, she is paid just the basic salary.   Write an algorithm to determine and print the salary of the worker.

48. SELECTION STRUCTURES Write an algorithm to accept any two numbers, the first a numerator and the second the denominator. If the second is equal to zero print “Cannot divide by 0”. Otherwise divide the first number by the second and print the answer.

49. SELECTION STRUCTURES A teacher has realized an error in his marking of students’ scripts. He has therefore decided to credit all students who got 55 marks and under with an additional 10 marks. Those who got more than 55 would be credited with an additional 15 marks. Write an algorithm to accept the mark from a student in a class. Calculate and print the student’s adjusted mark.

50. SELECTION STRUCTURES A store offers customers a discount of 15% if the cost of any item purchased is equal to or exceeds $200.00. Should the cost be less than $200.00 however, then a 5% discount is applied. Write an algorithm to accept the cost of an item. Apply the relevant discount and calculate and print the net cost (cost – discount).