The document describes how to use flowcharts to visually represent algorithms. It provides examples of flowcharts for common algorithms like reading in a number and printing it, checking if a number is odd or even, finding the largest of two or three numbers, printing numbers from 1 to 5, adding numbers from 1 to 5, and checking if a number is prime. The flowcharts use standard symbols like rectangles for steps, diamonds for decisions, and arrows to show the flow. They demonstrate how to represent variables, assignments, comparisons, and other programming constructs visually in a simple and clear way for developers.

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?

4. Flowcharts
• So let’s say we want to express the
following algorithm:
– Read in a number and print it out.

5. START

6. START
Read in A

7. START
Read in A
Print A

8. START
Read in A
Print A
END

9. Flowcharts
• So let’s say we want to express the
following algorithm:
– Read in a number and print it out double the number.

10. START

11. START
Read in A

12. START
Read in A
Print A*2

13. START
Read in A
Print A*2
END

14. Or alternatively...

15. START

16. START
Read in A

17. START
Read in A
B = A*2

18. START
Read in A
B=A*2
can be
B = A*2 read as
“B gets the
value of A
multiplied by 2”

19. START
Read in A
B = A*2
Print B

20. START
Read in A
B = A*2
Print B
END

21. Flowcharts
• So let’s say we want to express the
following algorithm:
– Read in a number, check if it is odd or even.

22. START

23. START
Read in A

24. START
Read in A
Does A/2
give a
remainder?

25. START
Read in A
Does A/2
Print “It’s Odd” Yes
give a
remainder?

26. START
Read in A
Does A/2 No
Print “It’s Odd” Yes Print “It’s Even”
give a
remainder?

27. START
Read in A
Does A/2 No
Print “It’s Odd” Yes Print “It’s Even”
give a
remainder?
END

28. 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.

29. START

30. START
Read in A and B

31. START
Read in A and B
A>B?

32. START
Read in A and B
Print A Yes
A>B?

33. START
Read in A and B
Yes No
Print A A>B? Print B

34. START
Read in A and B
Yes No
Print A A>B? Print B
END

35. 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.

36. START

37. START
Read in A, B and C

38. START
Read in A, B and C
A>B?

39. START
Read in A, B and C
Yes
A>C? A>B?

40. START
Read in A, B and C
Yes No
A>C? A>B? B>C?

41. START
Read in A, B and C
Yes No
A>C? A>B? B>C?
No No
Print C

42. START
Read in A, B and C
Yes Yes No
A>C? A>B? B>C?
No No
Print A Print C

43. START
Read in A, B and C
Yes Yes No Yes
A>C? A>B? B>C?
No No
Print A Print C Print B

44. START
Read in A, B and C
Yes Yes No Yes
A>C? A>B? B>C?
No No
Print A Print C Print B
END

45. Flowcharts
• So let’s say we want to express the
following algorithm:
– Print out the numbers from 1 to 5

46. START

47. START
Print 1

48. START
Print 1
Print 2

49. START
Print 1
Print 2
Print 3

50. START
Print 1
Print 2
Print 3
Print 4

51. START
Print 1
Print 2
Print 3
Print 4
Print 5

52. START
Print 1
Print 2
Print 3
Print 4
Print 5
END

53. Or alternatively...

54. 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)

55. START

56. START
A=1

57. START
A=1
Is A==6?

58. START
A=1
No
Is A==6? Print A

59. START
A=1
A=A+1
No
Is A==6? Print A

60. START
A=1
A=A+1
No
Is A==6? Print A

61. START
A=1
A=A+1
No
Is A==6? Print A
Yes
END

62. Flowcharts
• So let’s say we want to express the
following algorithm:
– Add up the numbers 1 to 5

63. Flowcharts T=5
• But first a few points;
• If I say T = 5, that means “T gets the value
5”

64. Flowcharts T=5
• But first a few points;
• If I say T = 5, that means “T gets the value
5”
T

65. Flowcharts T=5
• But first a few points;
• If I say T = 5, that means “T gets the value
5”
5
T

66. Flowcharts T=X
• If I say T = X, that means “T gets the value
of whatever is in the variable X”

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.

68. 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

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”

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.

71. 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

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”

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
• X stays at 9

74. 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)

75. Flowcharts
• So let’s say we want to express the
following algorithm:
– Add up the numbers 1 to 5

76. START

77. START
Total = 0

78. START
Total = 0
A=1

79. START
Total = 0
A=1
Is A==6?

80. START
Total = 0
A=1
No
Is A==6? Total = Total + A;

81. START
Total = 0
A=1
A=A+1
No
Is A==6? Total = Total + A;

82. START
Total = 0
A=1
A=A+1
No
Is A==6? Total = Total + A;
Yes
END

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.

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?

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.

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.

87. 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.

88. 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

89. 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.

90. START

91. START
Read in A

92. START
Read in A
B = A -1

93. START
Read in A
B = A -1
Is B = = 1?

94. START
Read in A
B = A -1
No
Is B = = 1?

95. START
Read in A
B = A -1
No
Is B = = 1?
Does
A/B give a
remainder?

96. START
Read in A
B = A -1
No
Is B = = 1?
Yes
Does
A/B give a
remainder?

97. START
Read in A
B = A -1
B=B-1 No
Is B = = 1?
Yes
Does
A/B give a
remainder?

98. START
Read in A
B = A -1
B=B-1 No
Is B = = 1?
Yes
Does
A/B give a
remainder?

99. START
Read in A
B = A -1
B=B-1 No
Is B = = 1?
Yes
Does
A/B give a
remainder?
No
Print “Not Prime”

100. START
Read in A
B = A -1
B=B-1 No Yes
Is B = = 1? Print “Prime”
Yes
Does
A/B give a
remainder?
No
Print “Not Prime”

101. START
Read in A
B = A -1
B=B-1 No Yes
Is B = = 1? Print “Prime”
Yes
Does
A/B give a
remainder?
No
Print “Not Prime”
END

102. Symbols

103. Symbols

104. Symbols
Terminal Decision
Input/Output
Operation Connector
Process Module