cp1020 - week 4 making decisions. cp1020 ©university of wolverhampton - ian coulson & steve...

CP1020 - Week 4

Making Decisions

CP1020 ©University of Wolverhampton - Ian Coulson & Steve Garner

DecisionsExample:

Driving to a lecture you notice that you do not have much petrol left. You will need to fill up soon, and approaching you can see a petrol station. The price is reasonable, but you do not have a lot of time to spare, so don't want to have to queue to fill-up.

What would you do?

?


Decisions in Problem Solving

No!

Yes

"If the queue at the petrol station is short then I will stop there to fill up"

If (the queue at the petrol station is short)Then stop there and fill up

Decisions ...decisions..


You may decide:

"if the queue at the petrol station is short then I will stop there to fill up".

We could write the algorithm for this decision as:

If queue at petrol station is short then

stop there and fill up


Further Examples

if kettle has boiled then

make tea

if temperature less than 18 C. then

turn on central heating


General form of IF statements

IF condition THEN

<action>

ENDIF

IF, THEN and ENDIF are RESERVED words

condition is the “test”, if the answer is YES then we carry out the <action>


An example program

REM program : to demonstrate the IF statement

REM written by : S. Garner

REM date written 8/3/00

DIM iAge AS INTEGER

CLS ' clear the screen

INPUT "Please enter your age "; iAge

REM test the condition

IF iAge > 17 THEN

PRINT "You may vote at the next election"

END IF

END


Two way decisions

We frequently need to do either one thing or another, depending on some condition

If age is greater than 65 then

retire gracefully

else

keep working


Basic IF..THEN..ELSE

IF condition THEN

<action1>

ELSE

<action2>

ENDIF


Example program


DIM iMark AS INTEGER


INPUT "Please enter your mark(0-100) "; iMark

REM check mark for pass or fail

IF iMark < 40 THEN

PRINT "You have failed"

ELSE

PRINT "You have passed"

PRINT "Well Done!"

END IF

END


Testing

We now have more than one possible “route” through our code

We must TEST each of these!

We should also test the “boundary”


Test Data

Mark Expected Actual

Result Result

25 You have failed You have failed

60 You have passed You have passed

40 You have passed You have passed

39 You have failed You have failed


The condition statement

Usually we check a value.

The symbols used are:

= equal <> not equal

< less than <= less than or equal

> greater than >= Greater than or equal


Example Conditions

NOTE: Brackets help to clarify!

(iMark < 0)

(iAge >=18)

(iValueA = iValueB)

(iAge >= 16 AND iAge < 65)


More Complex Decisions 1

Problem:

You are looking for new employees for your company.One of the criteria is that the employee must be no younger than 16 and no older than 65.

Note: We have two conditions to satisfy: condition 1 is the candidate at least 16 years old? condition 2 is the candidate no older than 65?

Both condition 1 AND condition 2 must be satisfied "TRUE" in order to accept the candidate


More Complex Decisions 2

Algorithm:

Step1 Get age of candidate2 If ( age at least 16) AND (age less than

65 )2.1 Then candidate is eligible2.2 Else reject candidate

AND implies that both conditions must be true


The code

INPUT “How old is the candidate > ”; iCandidatesAge

If (iCandidatesAge >= 16) And (iCandidatesAge <= 65) Then Print “You are eligible to apply”

ElsePrint “You are outside the age range!”

End If


The OR condition

Alternatively test for ineligible candidates:

Step1 Get age of candidate2 If ( age less than 16) OR (age greater than 65 )

2.1 Then reject candidate2.2 Else candidate is eligible

OR implies that either one (or both) of the conditions needs to be satisfied


Another Example


REM written by : I Coulson

REM date written: 8/3/00

DIM iCandAge AS INTEGER


INPUT "Please enter your age "; iCandAge

IF ( iCandAge < 16) OR ( iCandAge > 65) THEN

PRINT ”Sorry you are outside the age range"

ELSE

PRINT “You are eligible to apply”

END IF

END


Problem - Student Grades

When a piece of work is marked, it is given a percentage mark which needs converting to a FAIL, PASS, MERIT or DISTINCTION.

A Fail Upto 40 A Pass 40 - 59 A Merit 60 - 79 A Distinction 80 +


Mark to Grade ConversionAlgorithm

Algorithm:Step1 Get a student's mark

2 If (mark is greater than 0) AND (mark less than 40)2.1 Then Grade is Fail

3 If (mark greater than or equal to 40) AND (mark is less than 60)3.1 Then Grade is Pass

4 If (mark is greater or equal to 60) AND (mark less than 80)4.1 Then Grade is Merit

5 If (mark is greater or equal to 80) AND (mark is no more than 100)5.1 Then Grade is Distinction

6 Display Grade


Mark to Grade Conversion Improved Algorithm Further improved algorithm:

Step1 Get a student's mark

2 If (mark is less than 40%)2.1 Then Grade is Fail2.2 Else If (mark is less than 60%)

2.2.1 Then Grade is Pass2.2.2 Else If (mark is less than 80%)

2.2.2.1 Then Grade is Merit2.2.2.2 Else Grade is Distinction

3 Display Grade

This is known as nesting decisions


The Program

Rem Author I Coulson

DIM iPercentage AS INTEGER

INPUT ”What percentage did you get "; iPercentage

IF iPercentage < 40 THEN

Print “Fail”

ELSEIF iPercentage < 60 THEN

Print “Pass”

ELSEIF iPercentage < 80 THEN

Print “Merit”

ELSEIF iPercentage >= 80 THEN

Print “Distinction”

END IF


Questions

1 Write an algorithm to decide if a salesman should get a bonus - he needs to have sold at least £3000 worth of goods in the month.

2 Alter the algorithm such that that the salesman earns 15% commission on all sales if sells more than £3000 worth of goods in a month, but only 5% if he sells less than that.

3 Write the code to print the appropriate comment to a runner finishing a race:

1st place - “well done you are the winner”

2nd place - “congratulations you are runner up”

3rd place - “good, you have finished third”

unplaced - “You’ve finished, well done”


End of lecture

cp1020 - week 4 making decisions. cp1020 ©university of wolverhampton - ian coulson & steve...

Documents

decisions slide

ian coulson steve garner

end slide

endif slide

petrol station

boundary slide

cp1020 week

garner rem date