algorithm

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algorithm

  1. 1. ALGORITHM
  2. 2. Definition: • Algorithm is a finite sequence of instructions required for producing the desired result. • It is also defined as “any problem whose solution can be expressed in a list of executable instruction.”
  3. 3. Characteristics: • The steps in the algorithm must be unambiguous . • It should be written in sequence. • Ensure that the algorithm will terminate. • It should conclude after a finite number of steps.
  4. 4. Quality of good algorithm: • Time • Memory • Accuracy • Sequence • Generality
  5. 5. Representation of algorithm: • Normal English -The algorithm is represented in step by step sequential order in normal English. • Flow chart- It is a pictorial representation of an algorithm. • Pseudo code –it is a formal design tool and utilized very well with the rules of structure design and programming.
  6. 6. Contd.. • Decision table- it is used to helps a lot in designing a specific segment of a design. • Program - it is represented as a program using any high level language.
  7. 7. Example • Addition of two numbers Step1: Start Step2: Read a, b Step3: Add the value of a with b and store the result in c. Step4: Display the value of c Step5: Stop
  8. 8. PSEUDO CODE
  9. 9. Definition: • Pseudo means imitates and code means instruction. • It is formal design tool. • It is also called Program Design Language.
  10. 10. Keywords • READ,GET • PRINT,DISPLAY • COMPUTE,CALCULATE
  11. 11. Guidelines for writing Pseudo code • Steps should be understandable • Capitalize the keyword. • Indent to show hierarchy. • End multiple line structure etc,.
  12. 12. Example READ a,b C=a+b WRITE C stop
  13. 13. Example READ a,b IF a>b PRINT a is greater ELSE PRINT b is greater ENDIF stop
  14. 14. Advantage & Disadvantage • It can be easily modified • It can be understood easily • Compare to flowchart it is difficult to understand the program logic.
  15. 15. Flowcharts • It is the pictorial representation of the algorithm. • A flow chart, or flow diagram, is a graphical representation of a process or system that details the sequencing of steps required to create output. • A flowchart is a picture of the separate steps of a process in sequential order.
  16. 16. Flowchart Symbols • Terminal symbol – It is used to represent the start, end of the program logic. • Input/Output – It is used for input or output. • Process Symbol – It is used to represent the calculations, data movements, initialization operations etc,.
  17. 17. • Decision Symbol – It is used to denote a decision to be made at that point • Flow lines – It is used to connect the symbols • Connectors – It is used to connect the flow lines.
  18. 18. Rules for preparing flowcharts • It should be simple. • Standard symbols should be used. • The flow lines should not intersect each others. • In case of complex flowcharts use the connectors symbols.
  19. 19. • Only one flow line should enter the process symbol and only one flow line should come out from a process symbol. • Only one flow line used with the terminal symbol. START STOP
  20. 20. • Only one flow line should enter the decision symbol and two or three flowlines may leave from the decision symbol.
  21. 21. Benefits of Flowcharts • Makes Logic Clear • Communication • Effective Analysis • Useful in coding • Useful in Testing etc,.
  22. 22. Limits of Flowcharts • It is difficult to use flowcharts for large program • Difficult to modify • Cost etc,.
  23. 23. Program control structures: • Program control structure are defined as the program statements that specifies the order in which statements are executed. • Types: – Sequence control structure – Selection control structure – Repetition control structure
  24. 24. • The instructions are computed in sequence i.e. it performs instruction one after another. • It uses top-down approach. Sequence control structure
  25. 25. Sequence control structure Flow chart Pseudo code Process 1 Process 2 Process nProcess 2 Process n Process 1
  26. 26. Example START C=a+b Print c Read a,b STOP
  27. 27. SELECTION CONTROL STRUCTURE • It is used for making decisions. • It allows the program to make a choice from alternative paths. • IF …THEN • IF …THEN… ELSE • CASE etc.,
  28. 28. IF…THEN Pseudo code Flow chart IF condition THEN process 1 . . END IF . . If condition NO YES Process 1
  29. 29. Example Start Read a If a>0 Print a is Positive Stop no yes
  30. 30. IF…THEN…ELSE Pseudo code Flowchart IF condition THEN process 1 . . ELSE process 2 . . END IF . . If condition YES NO Process 1 Process 2
  31. 31. Example Start Read a,b If a>b Print a is Greater Print b is Greater Stop no yes
  32. 32. CASE structure Pseudo code Flow chart . . CASE Type Case Type-1: Process 1 Case Type-2: Process 2 . . Case Type-n: Process n . . END CASE Type 1 Type 2 Type 3 Process 1 Process 2 Process 3 no no no yes yes yes
  33. 33. start stop Read m1,m2,m3 Avg=(m1+m2+m3)/3 If Avg>=60 If Avg>=50 If Avg>=35 Fail Print First Class Print Second Class Print Third Class Example: Finding the Grade
  34. 34. Repetition control structure(looping) • It is used to execute some instructions several time based on some condition. • WHILE loop • Do…WHILE loop etc.,
  35. 35. WHILE Loop Pseudo code Flow chart WHILE condition . . Body of the loop . . END WHILE Body of The loop condition no yes
  36. 36. Example Start Num=0 Num=Num+1 Print Num while Num<5 stop no yes
  37. 37. DO…WHILE Loop Pseudocode Flow chart DO . . Body of the loop . . WHILE condition . . END WHILE Body of The loop condition no yes
  38. 38. Example Start Num=0 Num=Num+1 Print Num while Num<5 stop no yes
  39. 39. Example: Finding the area of a circle Algorithm Step1: Start Step2: Read the value of r Step3: Calculate area = 3.14*r*r Step4: Print area Step5: Stop

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