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Algorithms, Flowchart and Pseudocode

Algorithms, Flowchart and Pseudocode. Original Source : http :// www.ftsm.ukm.my/zma/TK1914/05-Algorithms and Problem Solving.ppt. WHAT IS AN ALGORITHM?. An algorithm is a set of ordered steps for solving a problem. Examples: An algorithm for preparing breakfast.

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Algorithms, Flowchart and Pseudocode

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  1. Algorithms, Flowchart and Pseudocode Original Source : http://www.ftsm.ukm.my/zma/TK1914/05-Algorithms and ProblemSolving.ppt

  2. WHAT IS AN ALGORITHM? • An algorithm is a set of ordered steps for solving a problem. • Examples: • An algorithm for preparing breakfast. • An algorithm for converting Gregorian dates to Islamic dates. • An algorithm for calculating moon phase. • An algorithm for drawing a curve.

  3. Algorithm in Real Life • Consider the following … Problem: Baking a Cake How to solve: • Start • Preheat the oven at 180oC • Prepare a baking pan • Beat butter with sugar • Mix them with flour, eggs and essence vanilla • Pour the dough into the baking pan • Put the pan into the oven • End

  4. ‘Divide and Conquer’ Strategy in Algorithm Problem: Prepare a Breakfast 1. Start 2. Prepare a Breakfast 3. End

  5. ‘Divide and Conquer’ Strategy in Algorithm 1. Start 2. Prepare a Breakfast 2.1 Prepare a tuna sandwich 2.2 Prepare some chips 2.3 Make a cup of coffee 3. End

  6. ‘Divide and Conquer’ Strategy in Algorithm 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 2.3 Make a cup of coffee 3. End

  7. ‘Divide and Conquer’ Strategy in Algorithm 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 3. End

  8. ‘Divide and Conquer’ Strategy in Algorithm 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

  9. CLASS ACTIVITY 5.1 • Write a simple algorithm for withdrawing a sum of money at an ATM.

  10. WHY DO WE NEED TO BUILD ALGORITHMS? • If we wish to build a house, we need to design it first. • Can you think of some possible consequences of not designing a house before building it? • Similarly, computer programs (especially large and complex ones) need to be designed before they are written. • Can you think of some possible consequences of not designing a program before building it? • One of the things considered when designing a computer program is the algorithm which it will be based on.

  11. ALGORITHMS IN PROGRAM DESIGN • A computer program is built to solve a certain problem. Examples: 1. A program to calculate the grade obtained given a mark. 2. A program to convert a Gregorian date to an Islamic date. 3. A program to produce a document.

  12. Below are steps (in fact, an algorithm) for building a program to solve a particular problem: • Analyse the problem • Design a computer solution to the problem by developing an algorithm. • Write a computer program based on the algorithm. • Test the program.

  13. HOW TO SPECIFY AN ALGORITHM? • An algorithm must be specific enough so that it can be conveniently translated into a computer program (using C++, for example). • An algorithm can be specified: • Textually For example, using pseudo code (see later) • Graphically For example, using flowcharts or UML activity charts

  14. FLOWCHARTS • A flowchart is a graphical representation of the sequence of operations in a program. • An algorithm can be represented graphically using a flowchart.

  15. Semantic Symbol Start/End Process Input/Output Test Connector Flow of activities Flowchart notations

  16. Algorithm starts here Input data from user Perform the date conversion Display the result Algorithm ends here FLOWCHART: EXAMPLE 1 Start Input Gregorian date Convert Gregorian date to Islamic date Display Islamic date End

  17. Pseudocode • An outline of a program, written in a form that can easily be converted into real programming statements. It resembles the actual program that will be implemented later. However, it cannot be compiled nor executed. • Pseudocode normally codes the following actions: • Initialisation of variables • Assignment of values to the variables • Arithmetic operations • Relational operations

  18. Example of Pseudocode 1. Start 2. Read quantity 3. Read price_per_kg 4. price  quantity * price_per_kg 5. Print price 6. End

  19. CLASS ACTIVITY 5.2 • Draw a flowchart which represents the algorithm built in CA[5.1].

  20. FLOWCHART: EXAMPLE 2 Start • length, width and area are referred to as variables. • A variable is like a box in which a value can be stored Input length, width area←length X width Output area End

  21. FLOWCHART: EXAMPLE 3 • Selection Start Input height false true height > 1.6? Output “You are short!” Output “You are tall!” End

  22. stop = 1? FLOWCHART: EXAMPLE 4 • Repetition (looping) Start Output “Thank you!” Input stop false true End

  23. YOU SHOULD NOW KNOW… • what an algorithm is. • when an algorithm should be developed when building a computer program. • the basic steps in building a computer program to solve a problem. • what flowcharts are. • how to represent algorithms graphically using flowcharts.

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