Problem solving and design
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This document covers problem solving and design with a focus on computer systems, outlining learning objectives including algorithms, flowcharts, and validation techniques. It emphasizes the importance of top-down design, pseudocode, and the use of sub-routines and library routines in building effective software solutions. Various real-life applications and examples are provided to illustrate these concepts, along with methods for ensuring data accuracy and program reliability.
Problem solving and design
- 1. Sir Z@h!d Al! +971-568047507 +92-3242415561 Problem Solving and Design Chapter: 09
- 2. Sir Z@h!d Al! +971-568047507 +92-3242415561 Learning Objectives In this topic we will learn about: • computer systems and sub-systems • top-down design • structure diagrams • flowcharts • pseudocode • library routines • sub-routines • algorithms • standard methods of solution • test data • validation and verification • using trace tables • identifying and correcting errors • producing algorithms • the effectiveness of a solution.
- 3. Sir Z@h!d Al! +971-568047507 +92-3242415561 Introduction • In order to build a computer system that performs a specific task or solves a given problem, the task or problem has to be clearly defined, showing what is going to be computed and how it is going to be computed. • This topic introduces the tools and techniques that are used to design a software solution that together with the associated computer hardware will form a computer system.
- 5. Sir Z@h!d Al! +971-568047507 +92-3242415561 What is a computer system? • A computer system consists of software, data, hardware, communications and people that have been carefully chosen so that they work well together in order to build a computer system that performs a specific task. • HOT • Do we have a system other than computer systems? • Why we use system?
- 6. Sir Z@h!d Al! +971-568047507 +92-3242415561 What tools and techniques are used to develop a system? • Computer system is often divided up into sub-systems. 1. This division can be shown using top-down design to produce structure diagrams that demonstrate the modular construction of the system. 2. Each sub-system can be developed by a programmer as sub- routine or an existing library routine may be already available for use. 3. How each sub-routine works can be shown by using flowcharts or pseudocode.
- 7. Sir Z@h!d Al! +971-568047507 +92-3242415561 Top-down design • It is the breaking down of a computer system into a set of subsystems, then breaking each sub-system down into a set of smaller sub-systems, until each sub-system just performs a single action. • This is an effective way of designing a computer system to provide a solution to a problem, since each part of the problem is broken down into smaller more manageable problems. • The process of breaking down into smaller sub-systems is called ‘Stepwise Refinement’.
- 8. Sir Z@h!d Al! +971-568047507 +92-3242415561 Structure diagrams • The STRUCTURE DIAGRAM shows the design of a computer system in a hierarchical way, with each level giving a more detailed breakdown of the system into sub- systems.
- 9. Sir Z@h!d Al! +971-568047507 +92-3242415561 Real-life application • Alarm app for a smart phone • Consider the alarm app computer system for a smart phone. • Creating the solution This involves: 1. top-down design or stepwise refinement 2. algorithms, which can be represented as a. program flowcharts b. pseudocode • Using top-down design approach, this could be divided into three sub-systems, • setting the alarm, • checking for the alarm time, • sounding the alarm. • These sub-systems could then be further sub-divided; the structure diagram makes the process clearer.
- 10. Sir Z@h!d Al! +971-568047507 +92-3242415561 Real-life application • Structure diagram for alarm app
- 11. Sir Z@h!d Al! +971-568047507 +92-3242415561 Activity 1. A school wants to calculate the number of hours spent in school by a sample of students from time of arrival and departure data. Draw a structure diagram and a program flowchart for an algorithm with the following features: 2. Draw a structure diagram for cleaning your teeth.
- 12. Sir Z@h!d Al! +971-568047507 +92-3242415561 Solution • Calculating hours spent in school • Using top-down design approach, this system could be divided into three sub-systems, • For each student, enter the student’s name, the time of arrival and the time of departure. • Calculate the length of time each student spends in school. • Output the student’s name and the time spent in school.
- 13. Sir Z@h!d Al! +971-568047507 +92-3242415561 What is Flowcharts? • A flowchart is a type of diagram that represents an algorithm, workflow or process, showing the steps as boxes of various kinds, and their order by connecting them with arrows. This diagrammatic representation illustrates a solution model to a given problem. OR • A FLOWCHART shows diagrammatically the steps required for a task (sub-system) and the order that they are to be performed. These steps together with the order are called an ALGORITHM. • Flowcharts are an effective way to communicate the algorithm that shows how a system or sub-system works.
- 14. Sir Z@h!d Al! +971-568047507 +92-3242415561 What are flowcharts symbols and their use? Example
- 15. Sir Z@h!d Al! +971-568047507 +92-3242415561 HOTS - Pair Activity • Write a flowchart program which input two numbers and output the sum of these number • Write a flowchart program to input physics and English marks and output the total marks
- 16. Sir Z@h!d Al! +971-568047507 +92-3242415561 Critical Thinking - Pair Work 1. Write an algorithm in the form of a flowchart which takes temperatures input over a 100 day period (once per day) and outputs the number of days when the temperature was below 20C and the number of days when the temperature was 20C and above. 2. Write an algorithm in the form of a flowchart which: • inputs the top speeds (in km/hr) of 5000 cars • outputs the fastest speed and the slowest speed • outputs the average (mean) speed of all the 5000 cars
- 17. Sir Z@h!d Al! +971-568047507 +92-3242415561 • Algorithm in the form of a flowchart Critical Thinking - Pair Work
- 18. Sir Z@h!d Al! +971-568047507 +92-3242415561 What is an algorithm? • An algorithm is a self-contained sequence of actions to be performed to solve a problem. • Well-structured programs require a programming language to support the following program constructs: • sequence • selection • iteration
- 19. Sir Z@h!d Al! +971-568047507 +92-3242415561 What is pseudocode? • Pseudocode is an informal high-level description of the operating principle of a computer program or other algorithm. It uses the structural conventions of a normal programming language, but is intended for human reading rather than machine reading.
- 20. Sir Z@h!d Al! +971-568047507 +92-3242415561 Understand and use pseudocode • understand and use pseudocode for assignment, using ← • understand and use pseudocode, using the following commands and statements: • INPUT and OUTPUT (e.g. READ and PRINT) • totaling (e.g. Sum ← Sum + Number) • counting (e.g. Count ← Count + 1)
- 21. Sir Z@h!d Al! +971-568047507 +92-3242415561 Understand and use pseudocode / algorithm • understand and use pseudocode, using the following conditional statements: • IF … THEN … ELSE … ENDIF • CASE … OF … OTHERWISE … ENDCASE • understand and use pseudocode, using the following loop structures: • FOR … TO … NEXT • REPEAT … UNTIL • WHILE … DO … ENDWHILE • (Candidates are advised to try out solutions to a variety of different problems on a computer using a language of their choice; no particular programming language will be assumed in this syllabus.)
- 22. Sir Z@h!d Al! +971-568047507 +92-3242415561 HOTS - Algorithm Vs Pseudocode Vs Program • An algorithm is a well-defined procedure that allows a computer to solve a problem. • Pseudocode is a simple way of writing programming code in simple language like English. • A program is a sequence of instructions in a particular programming language for instance QBASIC or C++, written to perform a specified task on a computer.
- 23. Sir Z@h!d Al! +971-568047507 +92-3242415561 HOTS - Pair Activity •Write a algorithm program which input two numbers and output the sum of these number •Write a algorithm program to input physics and English marks and output the total marks
- 24. Sir Z@h!d Al! +971-568047507 +92-3242415561 Critical Thinking - Pair Work 1. Write an algorithm in the form of a pseudocode / flowchart which takes temperatures input over a 100 day period (once per day) and outputs the number of days when the temperature was below 20C and the number of days when the temperature was 20C and above. 2. Write an algorithm in the form of a pseudocode / flowchart which: • inputs the top speeds (in km/hr) of 5000 cars • outputs the fastest speed and the slowest speed • outputs the average (mean) speed of all the 5000 cars
- 25. Sir Z@h!d Al! +971-568047507 +92-3242415561 What is Library routines? • A LIBRARY ROUTINE is a set of programming instructions for a given task that is already available for use. • It is pre-tested and usually performs a task that is frequently required. • For example, the task „get time‟ in the checking- for-the-alarm time algorithm would probably be readily available as a library routine.
- 26. Sir Z@h!d Al! +971-568047507 +92-3242415561 What is Sub-routines? •A SUB-ROUTINE is a set of programming instructions for a given task that forms a subsystem, not the whole system. •Sub-routines written in high-level programming languages are called „procedures‟ or „functions‟ depending on how they are used.
- 27. Sir Z@h!d Al! +971-568047507 +92-3242415561 What is Test Data? Why it is important ? • Test data is the data that is used in tests of a program or system. • In order to test a program we need to enter some data for testing most of the features. Any such specifically identified data which is used in tests is known as test data. • There are following three types of test data: • 1. Normal Data • 2. Extreme Data • 3. Abnormal Data
- 28. Sir Z@h!d Al! +971-568047507 +92-3242415561 Difference between Normal, Extreme and Abnormal Data Test Case Explanation Example where a score should be between 0 and 50 Normal Data that you would expect to work or be accepted and that lies within the range 2, 45 Extreme Data at the lower and upper limits of the range 0, 50 Abnormal Data that should not be accepted by the program -7, 51, Ahmed
- 29. Sir Z@h!d Al! +971-568047507 +92-3242415561 What is Rogue Values? • A value of input which is used to halt / break to repetitive statement. OR • A sequence of inputs may continue until a specific value is arrived / input. This value is called a rogue value and must be a value which would not normally arise. • A rogue value lets the computer know that a sequence of input values has come to an end.
- 30. Sir Z@h!d Al! +971-568047507 +92-3242415561 Pair Work Activity • A number of marks are to be input (terminated by a rogue value of -1). How many of them are over 50? • Counter = 0 • INPUT Marks • REPEAT • IF Marks >50 THEN counter = counter +1 • INPUT Marks • UNTIL Marks=-1 • OUTPUT counter
- 31. Sir Z@h!d Al! +971-568047507 +92-3242415561 How readable is your code? • Often programmers will work on each other's code. So you need to write your code so that it can be read and understood by others. You also need to be able to understand it if you come back to it months or years later. There are a few techniques you can use to help with this: • Internal commentary • Meaningful identifiers (variable names) • Indentation • White Space
- 32. Sir Z@h!d Al! +971-568047507 +92-3242415561 What kind of test data would be used to find out if a program works under regular circumstances? a) Normal b) Extreme c) Exceptional
- 33. Sir Z@h!d Al! +971-568047507 +92-3242415561 How to make sure that there is no error in the data? • Data verification and data validation are two methods of making sure no errors occur in the data before processing takes place. (Make sure you know the difference between them!)
- 34. Sir Z@h!d Al! +971-568047507 +92-3242415561 What is Data Verification? • Typing data into a computer from a data capture form is called transcribing. If an error is made it is a transcription error. • Verification is done to eliminate transcription errors. • Methods of verification... Proof reading A visual check by eye that no errors have been made. This is sometimes done by printing out data that has been input, and sending it back to the source of the data to check. For example, printed proofs of the pages of a book may be sent back to the author for checking. Double- keying This is a check to see if data has been keyed in correctly. The data is keyed in twice, and the computer will only accept the data for processing if the two versions are identical.
- 35. Sir Z@h!d Al! +971-568047507 +92-3242415561 What is Validation? • Validation is the automated checking by a program that data is reasonable before it is accepted into a computer system. Different types of check may be used on the same piece of data; • A check to see if data is 'valid' before it is processed that it is sensible data. • There are a number of different data validation checks which can be carried out. Following are some of them:
- 36. Sir Z@h!d Al! +971-568047507 +92-3242415561 Types of Validations Validation type How it works Example usage Check digit the last one or two digits in a code are used to check the other digits are correct bar code readers in supermarkets use check digits Format check checks the data is in the right format a National Insurance number is in the form LL 99 99 99 L where L is any letter and 9 is any number Length check checks the data isn't too short or too long a password which needs to be eight letters long Lookup table looks up acceptable values in a table there are only seven possible days of the week Presence check checks that data has been entered into a field in most databases a key fieldcannot be left blank Range check checks that a value falls within the specified range number of hours worked must be less than 50 and more than 0 Spell check looks up words in a dictionary when word processing
- 37. Sir Z@h!d Al! +971-568047507 +92-3242415561 Challenge!!! Individual work • Write an pseudocode for range check. • Draw the flow chart for the range check. • Write an pseudocode for presence check. • Draw the flow chart for the presence check. • Write an pseudocode for length check. • Draw the flow chart for the length check. • Try same for other varification and validation checks like double keying etc.