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Fundamentals of Programming Chapter 3
- 1. CHAPTER 3 ALGORITHMS PROG0101 FUNDAMENTALS OF PROGRAMMING C H A P T E R 1 O V E R V I E W O F C O M P U T E R S A N D L O G I C PROG0101 FUNDAMENTALS OF PROGRAMMING PROG0101 FUNDAMENTALS OF PROGRAMMING CHAPTER 3 ALGORITHM
- 2. 2 Introduction to Algorithms A sequence of instructions. A procedure or formula for solving a problem. It was created mathematician, Mohammed ibn-Musa al-Khwarizmi. Often used for calculation, data processing and programming. Algorithms can be expressed in any language.
- 3. 3 Introduction to Algorithms Algorithms for making things will often be divided into sections; the parts/components/ingredients (inputs) required to accomplish the task actions/steps/methods (processing) to produce the required outcome (output). For example to build a model car, the parts (inputs) are needed plus instructions on how to assemble the car (processing) and the result is the car (output).
- 4. 4 Types of Algorithms Two types of Algorithm: Pseudocode Flow chart
- 5. 5 Pseudocode Pseudocode (which means fake code, because its not really programming code) specifies the steps required to accomplish the task. Pseudocode is a type of structured English that is used to specify an algorithm. Pseudocode cannot be compiled nor executed, and there are no real formatting or syntax rules.
- 6. 6 Pseudocode Example of Pseudocode: Ready and open subscriber file Get a record Do while more records If current subscriber subscription count is > 3 then Output the record Get another record end
- 7. 7 Pseudocode Advantages of Pseudocode Reduced complexity. Increased flexibility. Ease of understanding.
- 8. 8 Pseudocode Why is Pseudocode Necessary? The programming process is a complicated one. You must first understand the program specifications. Then you need to organize your thoughts and create the program. You must break the main tasks that must be accomplished into smaller ones in order to be able to eventually write fully developed code. Writing Pseudocode will save you time later during the construction & testing phase of a program's development.
- 9. 9 Pseudocode How to Write Pseudocode Statements? 1. A computer can receive information Read (information from a file) Get (information from the keyboard) 2. A computer can put out information Write (information to a file) Display (information to the screen)
- 10. 10 Pseudocode How to Write Pseudocode Statements? 3. A computer can perform arithmetic Use actual mathematical symbols or the words for the symbols Example: Add number to total Total = total + number +, -, *, / Calculate, Compute also used
- 11. 11 Pseudocode How to Write Pseudocode Statements? 4. A computer can assign a value to a piece of data i. to give data an initial value Initialize, Set ii. to assign a value as a result of some processing *x=5+y iii. to keep a piece of information for later use Save, Store
- 12. 12 Pseudocode How to Write Pseudocode Statements? 5. A computer can compare two piece of information and select one of two alternative actions IF condition THEN some action ELSE alternative action ENDIF
- 13. 13 Pseudocode How to Write Pseudocode Statements? 6. A computer can repeat a group of actions WHILE condition (is true) some action ENDWHILE FOR a number of times some action ENDFOR
- 14. 14 Pseudocode Example 1: Program Specification: Pseudocode: Write a program that obtains two integer numbers from the user. It will print out the sum of those numbers. Prompt the user to enter the first integer Prompt the user to enter a second integer Compute the sum of the two user inputs Display an output prompt that explains the answer as the sum Display the result
- 15. 15 Pseudocode Example 2: Finding average of any three numbers. We might usually specify the procedure of solving this problem as “add the three numbers and divide by three”. Here, Read (or Ask) and Write (or Say) are implied. However in an algorithm, these steps have to be made explicit. Thus a possible algorithm is:
- 16. 16 Pseudocode Example 2: Step 1 Start Step 2 Read values of X, Y, Z Step 3 S = X + Y + Z Step 4 A = S / 3 Step 5 Write value of A Step 6 Stop
- 17. 17 Pseudocode Example 2: Or you can write like this: Step 1 Start Step 2 Read values of X, Y, Z Step 3 S = X + Y + Z Step 4 A = S / 3 Step 5 Write value of A Step 6 Stop
- 18. 18 Pseudocode Example 3: Finding square and cube. Step 1 Start Step 2 Read value of N Step 3 S = N * N Step 4 C = S * N Step 5 Write values of S, C Step 6 Stop
- 19. 19 Pseudocode Example 4: Finding biggest of two numbers. Step 1 Start Step 2 Read A, B Step 3 If A > B, then BIG = A, otherwise BIG = B Step 4 Write BIG Step 5 Stop
- 20. 20 Pseudocode Example 5: Calculate pay. Step 1 Start Step 2 Input hours Step 3 Input rate Step 4 pay = hours * rate Step 5 Print pay Step 6 End
- 21. 21 Pseudocode Exercise: Write a Pseudocode for these problems. 1. S = (A + B + C) / Y 2. Convert from Celsius to Fahrenheit. 3. Area of Circle (r2) 4. Volume of Sphere ( r3) 5. Average speed = 4 3 Distance traveled Time taken (Multiply by 9, then divide by 5, then add 32 )
- 22. 22 Flowchart A flowchart is a graphical representation of an algorithm. These flowcharts play a vital role in the programming of a problem and are quite helpful in understanding the logic of complicated and lengthy problems. Once the flowchart is drawn, it becomes easy to write the program in any high level language.
- 23. 23 Flowchart Flowchart A flowchart can therefore be used to: Define and analyze processes Build a step-by-step picture of the process for analysis, discussion, or communication Define, standardize or find areas for improvement in a process
- 25. 25 Flowchart Flowchart Symbols Start and End symbols Represented as lozenges, ovals or rounded rectangles Usually containing the word "Start" or "End", or another phrase signalling the start or end of a process, such as "submit enquiry" or "receive product".
- 26. 26 Flowchart Flowchart Symbols Arrows Showing what's called "flow of control" in computer science. An arrow coming from one symbol and ending at another symbol. Represents that control passes to the symbol the arrow points to.
- 27. 27 Flowchart Flowchart Symbols Processing steps Represented as rectangles. Examples: “Add 1 to X"; "replace identified part"; "save changes" or similar.
- 28. 28 Flowchart Flowchart Symbols Input/Output Represented as a parallelogram. Examples: Get X from the user; display X.
- 29. 29 Flowchart Flowchart Symbols Conditional or decision Represented as a diamond (rhombus). These typically contain a Yes/No question or True/False test.
- 30. 30 Algorithms Flowchart Symbols Display Indicates a process flow step where information is displayed to a person (e.g., PC user, machine operator).
- 31. 31 Flowchart Rules for Flowchart 1. Every flow chart has a START symbol and a STOP symbol. 2. The flow of sequence is generally from the top of the page to the bottom of the page. This can vary with loops which need to flow back to an entry point. 3. Use arrow-heads on connectors where flow direction may not be obvious. 4. There is only one flow chart per page.
- 32. 32 Flowchart Rules for Flowchart 5. A page should have a page number and a title. 6. A flow chart on one page should not break and jump to another page 7. A flow chart should have no more than around 15 symbols (not including START and STOP).
- 33. 33 Flowchart Advantages of Using Flowcharts 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 analysed 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.
- 34. 34 Flowchart Advantages of Using Flowcharts 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.
- 35. 35 Flowchart Basic Control Structures Sequence Selection Loop
- 36. 36 Flowchart Basic Control Structures Sequence Steps that execute in sequence are represented by symbols that follow each other top to bottom or left to right. Top to bottom is the standard.
- 38. 38 Flowchart Basic Control Structures Selection/Branching Once the condition is evaluated, the control flows into one of two paths. Once the conditional execution is finished, the flows rejoin before leaving the structure.
- 40. 40 Flowchart Basic Control Structures Loop Either the processing repeats or the control leaves the structure. Notice that the return line joins the entry line before the question.
- 42. 42 Flowchart Example 1: Algorithm: Input: two numbers x and y Output: the average of x and y Steps: 1. input x 2. input y 3. sum = x + y 4. average = sum /2 5. output average
- 44. 44 Flowchart Example 2: Draw a flowchart to find the largest of three numbers A, B, and C.
- 46. 46 Flowchart Exercise: Draw a flowchart diagram. 1. A program that compare the first number and second number and display which one is the biggest. 2. Login screen to check the Username and Password.