Transcript flowchart powerpoint

Flowchart
The art of drawing a road map
Symbols

Oval (“racetrack”)
 Start or Stop (Terminator)

Start
Calculate Avg
Rectangle
 Process (calculation, value assignment, etc)

Perform Tax
Calculation
Rectangle with double vertical sides
 A predefined process
 Allows you to represent something complicated at an early stage and basically show that “it goes here” in your
flow of activity

Get
TempCent
Rhomboid (slanted rectangle)
 Input / output (data)

Diamond
 Decision
Arrows indicate direction or “flow” of activity
 Small circle (possibly with letter inside)

 “on page” continuation

Home Plate
A
 “off page” continuation
AvgGrades
Age>
21?
Flowchart
 Demonstrates a sequence of activities and decisions
 Can be used as a roadmap in writing code
 Certain shapes identify code “structures”
 Decision structures
 A condition which evaluates to True or False
 Asks a question which “directs” the continued flow of activity
 Repetition structures (loops)
 A return to a prior point in the flowchart
 NOTE: this return is based on a condition being either true or false
 While the shape asking the question is a diamond and could be an “IF”
statement, the fact that one of the branches from the diamond returns
to a prior point indicates that the conditional question asked is part of
a LOOP and not an IF
Flowchart
 Forces us to think about what we do
 We need to identify each discrete action (process) or question (decision) in order to solve
the problem
 Flowcharts can identify that we “missed” something
 We have a process which calculates “GROSSPAY”, and know that GROSSPAY requires
“Hoursworked” and “HourlyPay” as input, but we notice that prior to the calculation, we
never bothered to get HoursWorked (missing input)
 We’ve calculated a result “NETPAY”, however never display it to the user (output of our
solution)
 Flowcharts can identify a sequencing error
 We display a result prior to calculating it
 We can think about things more abstractly
 Calculate Grosspay
 If we know someone worked 10 hours at $15/hour the calculation is 10 x 15
 NOT abstract enough… it only works for that single case
 Work backwards. What does the 10 represent? [ Hoursworked]
 Use THAT name to represent any value given
ATM Password Validation
 The user gets 3 attempts to
provide the valid password
 If valid
 Go to the process transaction “offpage” routine
 If it’s the 3rd failed attempt
 Stop!
 Decision
 “Valid” diamond
 Repetition
 3rd attempt question is part of
the LOOP, and not simply an IF
 How you can identify the
difference between which structure
to code (IF vs. LOOP)
IF statement / variations
 IF
 IF .. ELSEIF… ENDIF
blnPass=False
If Avg >=90 then
LG = “A”
ElseIf Avg >= 80
LG = “B”
ElseIf Avg >= 70
LG = “C”
Else
LG = “F”
End If
If AvgGrade > 65 then blnPass=TRUE
 IF ..ELSE..ENDIF
If AvgGrade > 65 then
blnPass=True
Else
blnPass = False
End If
Filling in symbols
 Processes
 Use a “verb” or action word
 Think of each process as its own little “IPO” (Input-Process-Output)
 Do you have all of the required inputs to do the process at that point in time?
 If not, maybe you missed a step somewhere
 Decisions
 True or false
 Comparison
 Age>21
 Counter <= 3
 State
 Grade exists?
Slow down!
 Draw a flowchart finding the average of 3 grades
 How would you do it with paper and pencil?
 Take the first grade
 Add the 2nd to the first grade
 Add the 3rd to that
 You’re “accumulating” (totaling) the grades
 In English… “I’m adding to the grade total”
 After grade total is calculated
 Calculate the final average by dividing it by the number of grades
(3)
 Show the answer
Average of 3 grades
Average of “n” grades
 You’ll still do the same process
 Except… you don’t now how many grades you have
 Count them!!! (GradeCount accumulator)
 You’ll keep counting and adding grades until….
 No more grades left (condition in your loop decision)
 Maybe ask “no more grades?” (true/false answer)
 Additional processes are bolded
 Altered decision is bold/dashed
Helpful hints
 Don’t keep track of totals in your mind
 “Store it” somewhere (write it on paper)
 Give it a name (something that represents that value)
 If you’re comparing something, like the highest grade
 It assumes that you’re keeping track of the last highest grade and
comparing the current grade to it
 Start off with HighGrade


Assign the lowest possible value to it BEFORE you start to compare the
grades you get
o This way, the very first grade will be higher
If the current grade is higher than the HighGrade, replace HighGrade
Finding the highest grade and average
Assignment
 Find the average height (in meters) of the students in your class
and display the result
 Also display the tallest and shortest students’ heights in meters
 All measurements are in terms of centimeters
 Final result to be displayed in meters (divide cm by 100)
 1 inch = 2.54 cm
 Heights vary between 150 and 200 cm
 Unknown number of students
 Approaches
 Find the average for 5 students
 When that works, change it to work for unknown number of students
 When that works, add the logic to find the tallest and shortest
students