Chapter 9 SB Answers

Cambridge International AS & A Level Computer Science
Chapter 9 Student Book Answers

What you should already know
1 Procedure – a single set of statements that can be grouped together and called in a program when
required, rather than repeated each time the statements are used.
2 Function – a single set of statements grouped together that return a value and are called in a
program when required, rather than repeated each time the statements are used.
3 Algorithm – an ordered set of steps to complete a task.
4 Structured English – using English words and mathematical operations to show the steps in an
algorithm.
5 Flowchart – a diagrammatical representation of the steps in an algorithm.
6 Pseudocode – shows the detailed logical steps in an algorithm using a set of keywords, declared
and typed identifiers and mathematical and logical operators.
Flowchart – Figure 9.3, Pseudocode before – Figure 9.3, Programs – before ACTIVITY 9F
Activity 9A
Possible solution
1 Ask for the number of sides
2 Ask for the length of each side
3 Calculate the internal angle of the polygon
4 Using a pencil and ruler draw a line of the required length
5 From the leftmost end of the line draw another line of the required length at the calculated angle
6 Repeat step 5 for number of sides − 1
Activity 9B
Counter is 2
MyChar is "A"
LetterValue is 65
StudentMark is 40
Percentage is 50
OldString is "Your mark is"
NewString is "Your mark is ninety-seven"
Activity 9C
1 else used in all three programming languages.
Python
# IF - single choice with alternative Python
MyValue = int(input("Please enter my value "))
YourValue = int(input("Please enter your value "))
if MyValue > YourValue:
print ("I win")
else:
print ("You win")
Cambridge International AS & A Level Computer Science 1

© Helen Williams and David Watson 2020

Cambridge International AS & A Level Computer Science Answers
VB
'IF - single choice with alternative VB

Module Module1
Sub Main()
Dim MyValue, YourValue As Integer

Console.Write("Please enter my value ")
MyValue = Integer.Parse(Console.ReadLine())
Console.Write("Please enter your value ")
YourValue = Integer.Parse(Console.ReadLine())
If MyValue > YourValue Then
Console.WriteLine("I win")
Else
Console.Writeline("You win")
End If
Console.ReadKey() 'wait for keypress
End Sub
End Module
Java
//IF - single choice with alternative Java

import java.util.Scanner;
class IFProgramWithAlt
{
public static void main(String args[])
{
Scanner myObj = new Scanner(System.in);
System.out.println("Please enter my value ");

int MyValue = myObj.nextInt();
System.out.println("Please enter your value ");
int YourValue = myObj.nextInt();
if (MyValue > YourValue)

{
System.out.println("I win");
} else {
system.out.println("You win");
}
}
}


Python - does not have a case statement
# - Multiple choice Python

X=0
Y=0
Direction = input("Please Enter N, S, E or W ")
if Direction == "N":
X=X+1
elif Direction == "S":
X=X-1
elif Direction == "E":
Y=Y+1
elif Direction == "W":
Y=Y-1
else:
print("Error")
print(X,Y)
VB – uses Select Case and Case Else

'Select Case VB
Module Module1
Sub Main()
Dim X, Y As Integer
Dim Direction As String
X = 0
Y = 0
Console.Write("Please Enter N, S, E or W ")
Direction = Console.ReadLine()
Select Case Direction
Case "N"
Y = Y + 1
Case "S"
Y = Y - 1
Case "E"
X = X + 1
Case "W"
X = X - 1
Case Else
Console.WriteLine("Error")
End Select
Console.Write(X & " " & Y)
End Sub
End Module


Java – uses switch case and default

// Switch Case Java
public class CaseStatement
{
{
int X = 0,Y = 0;
System.out.println("Please Enter N, S, E or W ");

String Direction = myObj.next();
switch (Direction){
case "N":
Y = Y + 1;
break;
case "S":
Y = Y - 1;
break;
case "E":
X = X + 1;
break;
case "W":
X = X - 1;
break;
default:
System.out.println("Error");
}
System.out.println(X + " " + Y);
}
}
Activity 9D
FOR without step
Python - does not reach 10

# FOR - simple loop Python without step
for Counter in range (1,10):
print(Counter)


VB - does reach 10
'FOR - simple loop VB without step
Module Module1
Sub Main()
Dim Counter As Integer

For Counter = 1 To 10
Console.WriteLine(Counter)
Next
End Sub
End Module
Java - does reach 10 but always needs to include an increment

//FOR - simple loop Java always needs to include an increment
class FORProgramWithoutStep
{
{
for (int Counter = 1; Counter <= 10; Counter++)
{
System.out.println(Counter);
}
}
}
REPEAT UNTIL loop
Python - does not have a repeat loop
VB – uses Do and Loop Until
'REPEAT UNTIL loop

Module Module1
Sub Main()
Dim Number As Integer
Do
Console.Write("Please enter a positive number ")
Number = Console.ReadLine()
Loop Until Number > 0

End Sub
End Module


Java – uses a post condition while loop

//Post condition loop
class PostConditionLoop
{
{
int Number = 0;
do {
System.out.println("Please enter a positive number ");
Number = myObj.nextInt();
}
while (Number <= 0);
}
}
While loop
Python – uses while and indentation

# WHILE Python
Number = 0
while Number >= 0:
Number = int(input("Please enter a negative number "))
VB – uses While and End While

'WHILE loop
Module Module1
Sub Main()
Dim Number As Integer
Number = 0
While Number >= 0
Console.Write("Please enter a positive number ")
Number = Console.ReadLine()
End While
End Sub
End Module
Java – uses a pre-condition while loop

//Pre-condition while loop
class PreConditionWhileLoop
{
{
int Number = 0;
while (Number >= 0){
System.out.println("Please enter a negative number ");
Number = myObj.nextInt();
}
}
}


Activity 9E
Number  0
REPEAT
PRINT "Enter a number, your number must be between 10 and 20 or over
100"
INPUT Number
UNTIL (Number > 10 AND Number < 20) OR (Number > 100)
Activity 9F
DECLARE Password1, Password2 : STRING
DECLARE Counter : INTEGER
Counter  0
REPEAT
PRINT "Enter your password "
INPUT Password1
PRINT "Enter your password again "
INPUT Password1
Counter  Counter + 1
UNTIL (Counter = 3) OR (Password1 = Password2)
IF Password1 = Password2
THEN
OUTPUT "Password correct"
ELSE
OUTPUT "Password incorrect"
ENDIF
Identifier Name Description

Counter To count the number of attempts
Password1 To store the first password attempt
Password2 To store the second password attempt
Python
# three attempts at checking password
Counter = 0
Password1 = "Pass1"
Password2 = "Pass2"
while ((Counter != 3) and (Password1 != Password2)):
Password1 = input("Enter your password ")
Password2 = input("Enter your password again ")
Counter = Counter + 1
if Password1 == Password2:
print ("Password correct")
else:
print ("Password incorrect")



VB
'three attempts at checking password
Module Module1
Sub Main()
Dim Password1, Password2 As String
Dim Counter As Integer
Counter = 0
Do
Console.Write("Please enter password ")
Password1 = Console.ReadLine()
Console.Write("Please enter password again ")
Password2 = Console.ReadLine()
Counter = Counter + 1
Loop Until ((Counter = 3) Or (Password1 = Password2))
If Password1 = Password2 Then
Console.WriteLine("Password correct")
Else
Console.WriteLine("Password incorrect")
End If
End Sub
End Module
Java – note the use of .equals for string comparison

//three attempts at checking password
class ACTIVITY9F
{
{
int Counter = 0;
String Password1 = "Pass1", Password2 = "Pass2";
do {
System.out.println("Enter your password ");
Password1 = myObj.next();
System.out.println("Enter your password again ");
Password2 = myObj.next();
Counter = Counter + 1;
}
while ((!Password1.equals(Password2)) && (Counter != 3));
if (Password1.equals(Password2)){
System.out.println("Password correct");
} else {
System.out.println("Password incorrect");
}
}
}


Activity 9G
OUTPUT "Enter your personal best time in seconds "
INPUT PBTimeSeconds
IF TotalMarathonTimeSeconds < PBTimeSeconds
THEN
PBTimeSeconds  TotalMarathonTimeSeconds
ENDIF
OUTPUT "Your personal best time in seconds is ", PBTimeSeconds

PBTimeSeconds Personal Best time in seconds
Python
# checking personal best time
TotalMarathonTimeSeconds = 14400 #value to use for test
PBTimeSeconds = int(input("Enter your personal best time in seconds "))
if TotalMarathonTimeSeconds < PBTimeSeconds:
PBTimeSeconds = TotalMarathonTimeSeconds
print( "Your personal best time in seconds is ", PBTimeSeconds)
VB
'checking personal best time
Module Module1
Sub Main()
Dim TotalMarathonTimeSeconds, PBTimeSeconds As Integer
TotalMarathonTimeSeconds = 14400 'value to use for test
Console.Write("Enter your personal best time in seconds ")
PBTimeSeconds = Console.ReadLine()
If TotalMarathonTimeSeconds < PBTimeSeconds Then
PBTimeSeconds = TotalMarathonTimeSeconds
End If
Console.WriteLine("Your personal best time in seconds is " +
PBTimeSeconds.ToString())
End Sub
End Module



Java
//checking personal best time
class ACTIVITY9G
{
{
int TotalMarathonTimeSeconds = 14400;
System.out.println("Enter your personal best time in seconds");
int PBTimeSeconds = myObj.nextInt();
if ( TotalMarathonTimeSeconds < PBTimeSeconds){
PBTimeSeconds= TotalMarathonTimeSeconds;
}
System.out.println("Your personal best time in seconds is " +
PBTimeSeconds);
}
}
Activity 9H
DECLARE Mark : INTEGER
DECLARE Grade, Reply : STRING
REPEAT
OUTPUT "Enter your exam mark"
INPUT Mark
IF Mark < 40
THEN
Grade  "Fail"
ELSE
IF Mark < 60
THEN
Grade  "Pass"
ELSE
IF Mark < 80
THEN
Grade  "Merit"
ELSE
Grade  "Distinction"
ENDIF
ENDIF
ENDIF
OUTPUT "Your grade is ", Grade
OUTPUT "Enter another exam mark Y/N "
INPUT Reply
UNTIL Reply <> "Y"

Mark Exam mark
Grade Exam grade
Reply Check for another mark


Python
# more than one mark
Reply = "Y"
while Reply == "Y":
Mark = int(input("Enter your exam mark "))
if Mark < 40:
Grade = "Fail"
elif Mark < 60:
Grade = "Pass"
elif Mark < 80:
Grade = "Merit"
else:
Grade = "Distinction"
print( "Your grade is ", Grade)
Reply = input("Enter another exam mark Y/N ")
VB
'more than one mark
Module Module1
Sub Main()
Dim Mark As Integer
Dim Grade, Reply As String
Reply = "Y"
Do
Console.Write("Enter your exam mark ")
Mark = Console.ReadLine()
Select Case Mark
Case 0 To 39
Grade = "Fail"
Case 40 To 59
Grade = "Pass"
Case 60 To 79
Grade = "Merit"
Case 80 To 100
Grade = "Distinction"
End Select
Console.WriteLine("Your Grade is " + Grade)
Console.Write("Enter another exam mark Y/N ")
Reply = Console.ReadLine()
Loop While (Reply = "Y")
End Sub
End Module



Java
//more than one mark
class ACTIVITY9H
{
{
String Grade, Reply;
Grade = "";
int Mark;
do {
System.out.println("Enter your exam mark");
Mark = myObj.nextInt();
if ( Mark < 40){
Grade = "Fail";
}
if ((Mark >= 40) && (Mark < 60) ){
Grade = "Pass";
}
if ((Mark >= 60) && (Mark < 80)) {
Grade = "Merit";
}
if (Mark > 80) {
Grade = "Distinction";
}
System.out.println("Your grade is " + Grade);
System.out.println("Enter another exam mark Y/N ");
Reply = myObj.next();
}
while (Reply.equals("Y"));
}
}
Activity 9I
DECLARE Shape : STRING
DECLARE Side, Base, Height, Radius : INTEGER
DECLARE Area : REAL
Area = 0
CONSTANT Pi = 3.142
OUTPUT "Please enter the shape (Square, Triangle, Circle) "
INPUT Shape
IF Shape = "Square"
THEN
OUTPUT "Please enter length of side "
INPUT Side
Area  Side * Side
ENDIF
IF Shape = "Triangle"
THEN
OUTPUT "Please enter length of base and height "
INPUT Base, Height
Area  (Base * Height) / 2
ENDIF
IF Shape = "Circle"
THEN

OUTPUT "Please enter length of radius "

INPUT Radius
Area  Pi * Radius * Radius
ENDIF
IF Area <> 0
THEN
OUTPUT "Area of ", Shape, " is ", Area
ENDIF
Python
# finding the area of a shape
Pi = 3.142
Area = 0.0
Shape = input("Please enter the shape ")
if Shape == "Square":
Side = int(input("Plese enter the length of the side "))
Area = Side * Side
elif Shape == "Triangle":
Base = int(input("Plese enter the length of the base "))
Height = int(input("Plese enter the length of the height "))
Area = (Base * Height) / 2
elif Shape == "Circle":
Radius = int(input("Plese enter the length of the radius "))
Area = Pi * Radius * Radius
if Area != 0:
print("Area of ", Shape, " is ", Area)
VB
' finding the area
Module Module1
Sub Main()
Dim Shape As String
Dim Area As Decimal
Dim Side, Base, Height, Radius As Integer
Const Pi As Decimal = 3.142
Area = 0.0
Console.Write("Please enter the shape ")
Shape = Console.ReadLine()
Select Case Shape

Case = "Square"
Console.Write("Please enter the side ")
Side = Console.ReadLine()
Area = Side * Side
Case = "Triangle"
Console.Write("Please enter the base ")
Base = Console.ReadLine()
Console.Write("Please enter the height ")
Height = Console.ReadLine()
Area = (Base * Height) / 2
Case = "Circle"
Console.Write("Please enter the radius ")
Radius = Console.ReadLine()
Area = Pi * Radius * Radius
End Select
If Area <> 0.0 Then


Console.WriteLine("Area of shape " + Shape + " is " + Area.ToString())

End If
End Sub
End Module
Java
// finding the area
public class ACTIVITY9I
{
{
int Side, Base, Height, Radius;
float Area = 0.0f;
float Pi = 3.142f;
System.out.println("Please enter the shape ");

String Shape = myObj.next();
switch (Shape){
case "Square":
System.out.println("Please enter the side ");
Side = myObj.nextInt();
Area = Side * Side;
break;
case "Triangle":
System.out.println("Please enter the base ");
Base = myObj.nextInt();
System.out.println("Please enter the height ");
Height = myObj.nextInt();
Area = (Base * Height) / 2;
break;
case "Circle":
System.out.println("Please enter the radius ");
Radius = myObj.nextInt();
Area = Pi * Radius * Radius;
}
if (Area != 0.0) {
System.out.println("Area of " + Shape + " is " + Area);
}
}
}



End of chapter questions

1 See Key terms 9.2.
2 See Section 9.1.
3 See Section 9.2.5.
4 a) 40 b) 314.2 c) Z not declared error d) True.
5 a) i) 13 or 14 ii) 07, 11 or 19 iii) 01 to 24
b)
Choice Store Menu Choice
Temperature Store temperature input
ConvertedTemperature Store converted temperature
c) Use a variable Try
01 Try  0
02 REPEAT
03 OUTPUT" Menu Temperature Conversion"
04 OUTPUT" Celsius to Fahrenheit 1"
05 OUTPUT" Fahrenheit to Celsius 2"
06 OUTPUT" Exit 3"
07 OUTPUT" Enter choice"
08 IF Choice = 1 OR Choice = 2
09 THEN
10 OUTPUT"Enter temperature"
11 INPUT Temperature
12 IF Choice = 1
13 THEN
14 ConvertedTemperature  1.8*Temperature + 32
15 ELSE
16 ConvertedTemperature  (Temperature – 32) * 5 / 9
17 ENDIF
18 OUTPUT "Converted temperature is ", ConvertedTemperature
19 ELSE
20 IF Choice <> 3
21 THEN
22 OUTPUT "Error in choice"
23 Try  Try + 1
24 ENDIF
25 ENDIF
26 UNTIL Choice = 3 OR Try = 3


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Cambridge International AS & A Level Computer Science

Chapter 9 Student Book Answers

Cambridge International AS & A Level Computer Science 1

'IF - single choice with alternative VB

Dim MyValue, YourValue As Integer

//IF - single choice with alternative Java

System.out.println("Please enter my value ");

if (MyValue > YourValue)

Cambridge International AS & A Level Computer Science 2

Python - does not have a case statement

# - Multiple choice Python

VB – uses Select Case and Case Else

Cambridge International AS & A Level Computer Science 3

Java – uses switch case and default

System.out.println("Please Enter N, S, E or W ");

FOR without step

Python - does not reach 10

Cambridge International AS & A Level Computer Science 4

Dim Counter As Integer

Java - does reach 10 but always needs to include an increment

REPEAT UNTIL loop

Python - does not have a repeat loop

VB – uses Do and Loop Until

'REPEAT UNTIL loop

Loop Until Number > 0

Cambridge International AS & A Level Computer Science 5

Java – uses a post condition while loop

Python – uses while and indentation

VB – uses While and End While

Java – uses a pre-condition while loop

Cambridge International AS & A Level Computer Science 6

Identifier Name Description

Cambridge International AS & A Level Computer Science 7

Java – note the use of .equals for string comparison

Cambridge International AS & A Level Computer Science 8

Identifier Name Description

Cambridge International AS & A Level Computer Science 9

Identifier Name Description

Cambridge International AS & A Level Computer Science 10

Cambridge International AS & A Level Computer Science 11

OUTPUT "Please enter length of radius "

Select Case Shape

Cambridge International AS & A Level Computer Science 13

Console.WriteLine("Area of shape " + Shape + " is " + Area.ToString())

Scanner myObj = new Scanner(System.in);

System.out.println("Please enter the shape ");

Cambridge International AS & A Level Computer Science 14

End of chapter questions

c) Use a variable Try

Cambridge International AS & A Level Computer Science 15

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