Transcript
pseudocode and Flowchart
MCS 1Tariq Ali
What is pseudocode?List of steps written in EnglishLike the instructions for a recipeMust be in the right sequence
Imagine saying “bake the cake” and then “mix it up”
Sample PseudocodeTask: add two numbersPseudocode:
Start Get two numbers
Get first number Get second number
Add themPrint the answerEnd
Invitation to Computer Science, Java Version, Third Edition 4
PseudocodeEnglish language constructs modeled to
look like statements available in most programming languages
Steps presented in a structured manner (numbered, indented, and so on)
No fixed syntax for most operations is required
Invitation to Computer Science, Java Version, Third Edition 5
Pseudocode (continued)Less ambiguous and more readable than
natural language
Emphasis is on process, not notation
Well-understood forms allow logical reasoning about algorithm behavior
Can be easily translated into a programming language
Sample PseudocodeTask: add two numbersPseudocode:
Start Get two numbers
Get first number Get second number
Add themPrint the answerEnd
What does a flowchart look like?The pseudocode from the previous slide
would look like this as a flowchart:
Start
Get 2 numbers
Add them
Print answer
End
What are those funny symbols?
START/END
INPUT/OUTPUT
PROCESS
DECISION
What are those funny symbols?START/ENDUsed at the
beginning and end of each flowchart.
INPUT/OUTPUTShows when
information/data comes into a program or is printed out.
What are those funny symbols?
What are those funny symbols?PROCESSUsed to show
calculations, storing of data in variables, and other “processes” that take place within a program.
What are those funny symbols?
What are those funny symbols?DECISIONUsed to show that
the program must decide whether something (usually a comparison between numbers) is true or false. YES and NO (or T/F) branches are usually shown.
What are those funny symbols?
Y
N
X>7?
Another Sample: Calculating AgePseudocode:
Start Get year DOBCalculate age = (sysdate-DOB)Print ageIf age > 50 print OLDEnd
Another Sample: Calculating Age
FlowchartStart Get year bornCalculate agePrint ageIf age > 50 print OLDEnd
Get yr
Calc age
Print age
Age>50?OLD Y
N
Start
End
Self-CheckLook at the flowchart section below. If the
variable X is 5, what will print (K or 1st)?
X > 5?YN Print “1st”Print “K”
Self-CheckLook at the flowchart section below. If the
variable X is 5, what will print (K or 1st)?
X > 5?YN Print “1st”Print “K”
K will be printed. The answer to the question “Is X greater than 5?” is NO, since X is equal to (not greater than) 5.
Self-CheckChoose the correct
flowchart symbol for each of these statements.
AGE>65?
Calc. Tax
START
Print NAME
Self-CheckChoose the correct
flowchart symbol for each of these statements.
AGE>65?
Calc. Tax
START
Print NAME
ChallengeTry to write pseudocode and create a
flowchart for a program that calculates the average of three grades and prints the average.
The word GOOD should be printed only if the average is more than 80.
ChallengePossible pseudocode
StartGet three gradesAverage them (add all of them / number of
grads taken)Print AverageAverage>80?
If Yes, print GOODEnd
ChallengePossible
flowchart StartGet three gradesAverage themPrint AverageAverage>80?
If Yes, print GOODEnd
START
END
Get 3 grades
Calc avg
Print avg
Avg>80?GOODY
N
ChallengeTry to write pseudocode and create a
flowchart for a program that calculates the average of three grades and prints the average.
The word GOOD should be printed only if the average is more than 80.
ChallengePossible pseudocode
StartGet three gradesAverage themPrint AverageAverage>80?
If Yes, print GOODEnd
ChallengePossible
flowchart StartGet three gradesAverage themPrint AverageAverage>80?
If Yes, print GOODEnd
START
END
Get 3 grades
Calc avg
Print avg
Avg>80?GOODY
N
Algorithm for Computing Average Miles per Gallon
Write a program to do the task: Print a list of the numbers from 4 to 9, next to each number, print the square of the number.
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