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- 1. Flow Charting Damian Gordon
- 2. Introduction• We mentioned it already, that if we thing of an analyst as being analogous to an architect, and a developer as being analogous to a builder, then the most important thing we can do as analysts is to explain our designs to the developers in a simple and clear way.• How do architects do this?
- 3. Flowcharts• So let’s say we want to express the following algorithm: – Read in a number and print it out.
- 4. START
- 5. STARTRead in A
- 6. STARTRead in A Print A
- 7. STARTRead in A Print A END
- 8. Flowcharts• So let’s say we want to express the following algorithm: – Read in a number and print it out double the number.
- 9. START
- 10. STARTRead in A
- 11. STARTRead in APrint A*2
- 12. STARTRead in APrint A*2 END
- 13. Or alternatively...
- 14. START
- 15. STARTRead in A
- 16. STARTRead in AB = A*2
- 17. STARTRead in A B=A*2 can beB = A*2 read as “B gets the value of A multiplied by 2”
- 18. STARTRead in AB = A*2 Print B
- 19. STARTRead in AB = A*2 Print B END
- 20. Flowcharts• So let’s say we want to express the following algorithm: – Read in a number, check if it is odd or even.
- 21. START
- 22. STARTRead in A
- 23. STARTRead in A Does A/2 give aremainder?
- 24. START Read in A Does A/2Print “It’s Odd” Yes give a remainder?
- 25. START Read in A Does A/2 NoPrint “It’s Odd” Yes Print “It’s Even” give a remainder?
- 26. START Read in A Does A/2 NoPrint “It’s Odd” Yes Print “It’s Even” give a remainder? END
- 27. Flowcharts• So let’s say we want to express the following algorithm to print out the bigger of two numbers: – Read in two numbers, call them A and B. Is A is bigger than B, print out A, otherwise print out B.
- 28. START
- 29. STARTRead in A and B
- 30. STARTRead in A and B A>B?
- 31. START Read in A and BPrint A Yes A>B?
- 32. START Read in A and B Yes NoPrint A A>B? Print B
- 33. START Read in A and B Yes NoPrint A A>B? Print B END
- 34. Flowcharts• So let’s say we want to express the following algorithm to print out the bigger of three numbers: – Read in three numbers, call them A, B and C. • If A is bigger than B, then if A is bigger than C, print out A, otherwise print out C. • If B is bigger than A, then if B is bigger than C, print out B, otherwise print out C.
- 35. START
- 36. STARTRead in A, B and C
- 37. STARTRead in A, B and C A>B?
- 38. START Read in A, B and C YesA>C? A>B?
- 39. START Read in A, B and C Yes NoA>C? A>B? B>C?
- 40. START Read in A, B and C Yes NoA>C? A>B? B>C? No No Print C
- 41. START Read in A, B and CYes Yes No A>C? A>B? B>C? No No Print A Print C
- 42. START Read in A, B and CYes Yes No Yes A>C? A>B? B>C? No No Print A Print C Print B
- 43. START Read in A, B and CYes Yes No Yes A>C? A>B? B>C? No No Print A Print C Print B END
- 44. Flowcharts• So let’s say we want to express the following algorithm: – Print out the numbers from 1 to 5
- 45. START
- 46. STARTPrint 1
- 47. STARTPrint 1Print 2
- 48. STARTPrint 1Print 2Print 3
- 49. STARTPrint 1Print 2Print 3Print 4
- 50. STARTPrint 1Print 2Print 3Print 4Print 5
- 51. STARTPrint 1Print 2Print 3Print 4Print 5 END
- 52. Or alternatively...
- 53. Flowcharts A=A+1• If I say A = A + 1, that means “A gets the value of whatever is in itself, plus 1”• If A is 14• It becomes 15 14 +1 A (old) 15 A (new)
- 54. START
- 55. STARTA=1
- 56. START A=1Is A==6?
- 57. START A=1 NoIs A==6? Print A
- 58. START A=1 A=A+1 NoIs A==6? Print A
- 59. START A=1 A=A+1 NoIs A==6? Print A
- 60. START A=1 A=A+1 NoIs A==6? Print AYes END
- 61. Flowcharts• So let’s say we want to express the following algorithm: – Add up the numbers 1 to 5
- 62. Flowcharts T=5• But first a few points;• If I say T = 5, that means “T gets the value 5”
- 63. Flowcharts T=5• But first a few points;• If I say T = 5, that means “T gets the value 5” T
- 64. Flowcharts T=5• But first a few points;• If I say T = 5, that means “T gets the value 5” 5 T
- 65. Flowcharts T=X• If I say T = X, that means “T gets the value of whatever is in the variable X”
- 66. Flowcharts T=X• If I say T = X, that means “T gets the value of whatever is in the variable X”• So if X is 14, then T will get the value 14.
- 67. Flowcharts T=X• If I say T = X, that means “T gets the value of whatever is in the variable X”• So if X is 14, then T will get the value 14. 14 X 14 T
- 68. Flowcharts T=X+1• If I say T = X+1, that means “T gets the value of whatever is in the variable X plus one”
- 69. Flowcharts T=X+1• If I say T = X+1, that means “T gets the value of whatever is in the variable X plus one”• So if X is 14, T becomes 15, and X stays as 14.
- 70. Flowcharts T=X+1• If I say T = X+1, that means “T gets the value of whatever is in the variable X plus one”• So if X is 14, T becomes 15, and X stays as 14. +1 14 X 15 T
- 71. Flowcharts T=T+X• If I say T = T + X, that means “T gets the value of whatever is in itself plus whatever is in the variable X”
- 72. Flowcharts T=T+X• If I say T = T + X, that means “T gets the value of whatever is in itself plus whatever is in the variable X”• If T is 14 and X is 9• T becomes 23• X stays at 9
- 73. Flowcharts T=T+X• If I say T = T + X, that means “T gets the value of whatever is in itself plus whatever is in the variable X”• If T is 14 and X is 9• T becomes 23 14 9• X stays at 9 T(old) X 23 T(new)
- 74. Flowcharts• So let’s say we want to express the following algorithm: – Add up the numbers 1 to 5
- 75. START
- 76. STARTTotal = 0
- 77. STARTTotal = 0 A=1
- 78. STARTTotal = 0 A=1Is A==6?
- 79. STARTTotal = 0 A=1 NoIs A==6? Total = Total + A;
- 80. STARTTotal = 0 A=1 A=A+1 NoIs A==6? Total = Total + A;
- 81. STARTTotal = 0 A=1 A=A+1 NoIs A==6? Total = Total + A;Yes END
- 82. Flowcharts• So let’s say we want to express the following algorithm: – Read in a number and check if it’s a prime number.
- 83. Flowcharts• So let’s say we want to express the following algorithm: – Read in a number and check if it’s a prime number. – What’s a prime number?
- 84. Flowcharts• So let’s say we want to express the following algorithm: – Read in a number and check if it’s a prime number. – What’s a prime number? – A number that’s only divisible by itself and 1, e.g. 7.
- 85. Flowcharts• So let’s say we want to express the following algorithm: – Read in a number and check if it’s a prime number. – What’s a prime number? – A number that’s only divisible by itself and 1, e.g. 7. – Or to put it another way, every number other than itself and 1 gives a remainder, e.g. For 7, if 6, 5, 4, 3, and 2 give a remainder then 7 is prime.
- 86. Flowcharts• So let’s say we want to express the following algorithm: – Read in a number and check if it’s a prime number. – What’s a prime number? – A number that’s only divisible by itself and 1, e.g. 7. – Or to put it another way, every number other than itself and 1 gives a remainder, e.g. For 7, if 6, 5, 4, 3, and 2 give a remainder then 7 is prime. – So all we need to do is divide 7 by all numbers less than it but greater than one, and if any of them have no remainder, we know it’s not prime.
- 87. Flowcharts• So,• If the number is 7, as long as 6, 5, 4, 3, and 2 give a remainder, 7 is prime.• If the number is 9, we know that 8, 7, 6, 5, and 4, all give remainders, but 3 does not give a remainder, it goes evenly into 9 so we can say 9 is not prime
- 88. Flowcharts• So remember, – if the number is 7, as long as 6, 5, 4, 3, and 2 give a remainder, 7 is prime.• So, in general, – if the number is A, as long as A-1, A-2, A-3, A- 4, ... 2 give a remainder, A is prime.
- 89. START
- 90. STARTRead in A
- 91. STARTRead in AB = A -1
- 92. STARTRead in AB = A -1Is B = = 1?
- 93. START Read in A B = A -1No Is B = = 1?
- 94. START Read in A B = A -1 No Is B = = 1? Does A/B give aremainder?
- 95. START Read in A B = A -1 No Is B = = 1?Yes Does A/B give a remainder?
- 96. START Read in A B = A -1B=B-1 No Is B = = 1? Yes Does A/B give a remainder?
- 97. START Read in A B = A -1B=B-1 No Is B = = 1? Yes Does A/B give a remainder?
- 98. START Read in A B = A -1B=B-1 No Is B = = 1? Yes Does A/B give a remainder? No Print “Not Prime”
- 99. START Read in A B = A -1B=B-1 No Yes Is B = = 1? Print “Prime” Yes Does A/B give a remainder? No Print “Not Prime”
- 100. START Read in A B = A -1B=B-1 No Yes Is B = = 1? Print “Prime” Yes Does A/B give a remainder? No Print “Not Prime” END
- 101. Symbols
- 102. Symbols
- 103. Symbols Terminal DecisionInput/OutputOperation Connector Process Module

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