Chapter 9. Algorithm Design and Problem Solving

Question 1

Comments

Answer 1

// This is a comment

Question 2

Datatypes

Answer 2

• INTEGER a whole number
• REAL a number capable of containing a fractional part
• CHAR a single character
• STRING a sequence of zero or more characters
• BOOLEAN the logical values TRUE and FALSE
• DATE a valid calendar date

Question 3

Literals

Answer 3

• Integer Written as normal in the denary system, e.g. 5, –3
• Real Always written with at least one digit on either side of the decimal point, zeros being added if
  necessary, e.g. 4.7, 0.3, –4.0, 0.0
• Char A single character delimited by single quotes e.g. ꞌxꞌ, ꞌCꞌ, ꞌ@ꞌ
• String Delimited by double quotes. A string may contain no characters (i.e. the empty string)
  e.g. “This is a string”, “”
• Boolean TRUE, FALSE
• Date This will normally be written in the format dd/mm/yyyy. However, it is good practice to state
  explicitly that this value is of data type DATE and to explain the format (as the convention for
  representing dates varies across the world).

Question 4

Variable declarations

Answer 4

DECLARE <identifier> : <data>
DECLARE Counter : INTEGER
DECLARE TotalToPay : REAL
DECLARE GameOver : BOOLEAN</data></identifier>

Question 5

Constants

Answer 5

CONSTANT <identifier> = <value>
CONSTANT HourlyRate = 6.50
CONSTANT DefaultText = "N/A"</value></identifier>

Question 6

Assignments

Answer 6

<identifier> ← <value>
Counter ← 0
Counter ← Counter + 1
TotalToPay ← NumberOfHours * HourlyRate
</value></identifier>

Question 7

Declaring arrays

Answer 7

A one-dimensional array is declared as follows:
DECLARE <identifier>:ARRAY[<lower>:<upper>] OF <data>
A two-dimensional array is declared as follows:
DECLARE <identifier>:ARRAY[<lower1>:<upper1>,<lower2>:<upper2>] OF <data>
Example – array declarations
DECLARE StudentNames : ARRAY[1:30] OF STRING
DECLARE NoughtsAndCrosses : ARRAY[1:3,1:3] OF CHAR</data></upper2></lower2></upper1></lower1></identifier></data></upper></lower></identifier>

Question 8

Using arrays

Answer 8

StudentNames[1] ← “Ali”
NoughtsAndCrosses[2,3] ← ꞌXꞌ
StudentNames[n+1] ← StudentNames[n]
FOR Index ← 1 TO 30
StudentNames[Index] ← “”
NEXT Index

Question 9

Defining user-defined data types

Answer 9

Non-composite-Enumerated data types
TYPE <identifier> = (value1, value2, value3, ...)
TYPE Season = (Spring, Summer, Autumn, Winter)</identifier>

Pointer data types
TYPE TIntPointer = ^INTEGER
DECLARE MyPointer : TIntPointer

Composite datatype-Record
TYPE <identifier1>
DECLARE <identifier2> : <data>
DECLARE <identifier3> : <data>
...
ENDTYPE</data></identifier3></data></identifier2></identifier1>

TYPE StudentRecord
DECLARE LastName : STRING
DECLARE FirstName : STRING
DECLARE DateOfBirth : DATE
DECLARE YearGroup : INTEGER
DECLARE FormGroup : CHAR
ENDTYPE

Set
TYPE <identifier1> = SET OF <data>
DEFINE <identifier2> (value1, value2, value, … ) : <identifier1></identifier1></identifier2></data></identifier1>

TYPE LetterSet = SET OF CHAR
DEFINE Vowels (‘A’,’E’,’I’,’O’,’U’): LetterSet

Question 10

Using user defined data types

Answer 10

DECLARE Pupil1 : StudentRecord
DECLARE Pupil2 : StudentRecord
DECLARE Form : ARRAY[1:30] OF StudentRecord
DECLARE ThisSeason : Season
DECLARE NextSeason : Season
DECLARE MyPointer : TIntPointer
Pupil1.LastName ← “Johnson”
Pupil1.Firstname ← “Leroy”
Pupil1.DateOfBirth ← 02/01/2005
Pupil1.YearGroup ← 6
Pupil1.FormGroup ← ꞌAꞌ
Pupil2 ← Pupil1
FOR Index ← 1 TO 30
Form[Index].YearGroup ← Form[Index].YearGroup + 1
NEXT Index
ThisSeason ← Spring
MyPointer ← ^ThisSeason
NextSeason ← MyPointer^ + 1
// access the value stored at the memory address

Question 11

Input and output

Answer 11

INPUT <identifier>
OUTPUT <value(s)>
INPUT Answer
OUTPUT Score
OUTPUT "You have ", Lives, " lives left"</identifier>

Question 12

Arithmetic operations

Answer 12

+ Addition
– Subtraction
* Multiplication
/ Division (The resulting value should be of data type REAL, even if the operands are integers.)
DIV Integer division: Used to find the quotient (integer number before the decimal point) after division.
MOD or Modulus: The remainder that is left over when one number is divided by another

Question 13

Relational operations

Answer 13

> Greater than
< Less than
= Greater than or equal to
<= Less than or equal to
= Equal to
<> Not equal to
The result of these operations is always of data type BOOLEAN.

Question 14

String functions and operations

Answer 14

RIGHT(ThisString : STRING, x : INTEGER) RETURNS STRING
returns rightmost x characters from ThisString
Example: RIGHT(“ABCDEFGH”, 3) returns “FGH”
LENGTH(ThisString : STRING) RETURNS INTEGER
returns the integer value representing the length of ThisString
Example: LENGTH(“Happy Days”) returns 10
MID(ThisString : STRING, x : INTEGER, y : INTEGER) RETURNS STRING
returns a string of length y starting at position x from ThisString
Example: MID(“ABCDEFGH”, 2, 3) returns “BCD”
LCASE(ThisChar : CHAR) RETURNS CHAR
returns the character value representing the lower-case equivalent of ThisChar
If ThisChar is not an upper-case alphabetic character, it is returned unchanged.
Example: LCASE(ꞌWꞌ) returns ꞌwꞌ
UCASE(ThisChar : CHAR) RETURNS CHAR
returns the character value representing the upper-case equivalent of ThisChar
If ThisChar is not a lower-case alphabetic character, it is returned unchanged.
Example: UCASE(ꞌhꞌ) returns ꞌHꞌ
In pseudocode, the operator & is used to concatenate (join) two strings.
Example: “Summer” & “ “ & “Pudding” produces “Summer Pudding”

Question 15

Numeric functions

Answer 15

INT(x : REAL) RETURNS INTEGER
returns the integer part of x
Example: INT(27.5415) returns 27
RAND(x : INTEGER) RETURNS REAL
returns a random real number in the range 0 to x (not inclusive of x)
Example: RAND(87) may return 35.43

Question 16

If statements

Answer 16

IF <condition> THEN
<statement(s)>
ENDIF
IF <condition> THEN
<statement(s)>
ELSE
<statement(s)>
ENDIF</condition></condition>

*There are no elseif statements you have to use case or nest if statements

Question 17

CASE statements

Answer 17

CASE OF <identifier>
<value 1> : <statement1></statement1></identifier>

<statement2>
...
<value 2> : <statement1>
<statement2>
...
OTHERWISE : <statement1>
<statement2>
...
ENDCASE

Each value may be represented by a range, for example:
<value1> TO <value2> : <statement1>
<statement2>

INPUT Move
CASE OF Move
ꞌWꞌ : Position ← Position − 10
ꞌSꞌ : Position ← Position + 10
ꞌAꞌ : Position ← Position − 1
ꞌDꞌ : Position ← Position + 1
OTHERWISE : CALL Beep
ENDCASE
</statement2></statement1></value2></value1></statement2></statement1></statement2></statement1></statement2>

Question 18

FOR loops

Answer 18

FOR <identifier> ← <value1> TO <value2>
<statement(s)>
NEXT <identifier></identifier></value2></value1></identifier>

FOR <identifier> ← <value1> TO <value2> STEP <increment>
<statement(s)>
NEXT <identifier></identifier></increment></value2></value1></identifier>

Total ← 0
FOR Row ← 1 TO MaxRow
RowTotal ← 0
FOR Column ← 1 TO 10
RowTotal ← RowTotal + Amount[Row, Column]
NEXT Column
OUTPUT “Total for Row “, Row, “ is “, RowTotal
Total ← Total + RowTotal
NEXT Row
OUTPUT “The grand total is “, Total

Question 19

REPEAT loops

Answer 19

REPEAT
<statement(s)>
UNTIL <condition></condition>

REPEAT
OUTPUT “Please enter the password”
INPUT Password
UNTIL Password = “Secret”

Question 20

WHILE loops

Answer 20

WHILE <condition>
<statement(s)>
ENDWHILE</condition>

WHILE Number > 9
Number ← Number – 9
ENDWHILE

Question 21

Defining and calling procedures

Answer 21

PROCEDURE <identifier>(<param1> : <data>, <param2> : <data>...)
<statement(s)>
ENDPROCEDURE</data></param2></data></param1></identifier>

CALL <identifier>(value1, value2, ...)</identifier>

Question 22

Defining and calling functions

Answer 22

FUNCTION <identifier>() RETURNS <data>
<statement(s)>
ENDFUNCTION</data></identifier>

FUNCTION <identifier>(<param1> : <data>,</data></param1></identifier>

<param2> : <data>...) RETURNS <data>
<statement(s)>
ENDFUNCTION

FUNCTION Max(Number1 : INTEGER, Number2 : INTEGER) RETURNS INTEGER
IF Number1 > Number2 THEN
RETURN Number1
ELSE
RETURN Number2
ENDIF
ENDFUNCTION
OUTPUT "Penalty Fine = ", Max(10, Distance*2)
</data></data></param2>

Question 23

By value or by reference

Answer 23

If there are several parameters passed by the same method,
the BYVAL or BYREF keyword need not be repeated.
Example – passing parameters by reference
PROCEDURE SWAP(BYREF X : INTEGER, Y : INTEGER)
Temp ← X
X ← Y
Y ← Temp
ENDPROCEDURE

Question 24

Handling text files

Answer 24

OPENFILE <file> FOR <file>
The file identifier may be a literal string containing the file names, or a variable of type STRING that has been
assigned the file name.
The following file modes are used:
* READ for data to be read from the file
* WRITE for data to be written to the file. A new file will be created and any existing data in the file will
be lost.
* APPEND for data to be added to the file, after any existing data.</file></file>

A file should be opened in only one mode at a time.
Data is read from the file (after the file has been opened in READ mode) using the READFILE command as
follows:
READFILE <file>, <variable>
The variable should be of data type STRING. When the command is executed, the next line of text in the file
is read and assigned to the variable.
The function EOF is used to test whether there are any more lines to be read from a given file. It is called as
follows:
EOF(<file>)
This function returns TRUE if there are no more lines to read (or if an empty file has been opened in READ
mode) and FALSE otherwise.
Data is written into the file (after the file has been opened in WRITE or APPEND mode) using the WRITEFILE
command as follows:
WRITEFILE <file>, <data>
Files should be closed when they are no longer needed using the CLOSEFILE command as follows:
CLOSEFILE <file></file></data></file></file></variable></file>

Question 25

Handling random files

Answer 25

Random files are opened using the RANDOM file mode as follows: OPENFILE FOR RANDOM As with text files, the file identifier will normally be the name of the file. The SEEK command moves the file pointer to a given location: SEEK ,

The address should be an expression that evaluates to an integer which indicates the location of a record to be read or written. This is usually the number of records from the beginning of the file. It is good practice to explain how the addresses are computed. The command GETRECORD should be used to read the record at the file pointer: GETRECORD , When this command is executed, the record that is read is assigned to the variable which must be of the appropriate data type for that record (usually a user-defined type). The command PUTRECORD is used to write a record into the file at the file pointer: PUTRECORD , When this command is executed, the data in the variable is inserted into the record at the file pointer. Any data that was previously at this location will be replaced. DECLARE Pupil : Student DECLARE NewPupil : Student DECLARE Position : INTEGER NewPupil.LastName ← "Johnson" NewPupil.Firstname ← "Leroy" NewPupil.DateOfBirth ← 02/01/2005 NewPupil.YearGroup ← 6 NewPupil.FormGroup ← ꞌAꞌ OPENFILE "StudentFile.Dat" FOR RANDOM FOR Position ← 20 TO 10 STEP -1 SEEK "StudentFile.Dat", Position GETRECORD "StudentFile.Dat", Pupil SEEK "StudentFile.Dat", Position + 1 PUTRECORD "StudentFile.Dat", Pupil NEXT Position SEEK "StudentFile.Dat", 10 PUTRECORD "StudentFile.Dat", NewPupil CLOSEFILE "StudentFile.dat"

Question 26

Methods and properties

Answer 26

PRIVATE Attempts : INTEGER Attempts ← 3 PUBLIC PROCEDURE SetAttempts(Number : INTEGER) Attempts ← Number ENDPROCEDURE PRIVATE FUNCTION GetAttempts() RETURNS INTEGER RETURN Attempts ENDFUNCTION Methods will be called using object methods, for example: Player.SetAttempts(5) OUTPUT Player.GetAttempts()

Question 27

Constructors and inheritance

Answer 27

Constructors will be procedures with the name NEW. CLASS Pet PRIVATE Name : STRING PUBLIC PROCEDURE NEW(GivenName : STRING) Name ← GivenName ENDPROCEDURE ENDCLASS Inheritance is denoted by the INHERITS keyword; superclass/parent class methods will be called using the keyword SUPER, for example: CLASS Cat INHERITS Pet PRIVATE Breed: INTEGER PUBLIC PROCEDURE NEW(GivenName : STRING, GivenBreed : STRING) SUPER.NEW(GivenName) Breed ← GivenBreed ENDPROCEDURE ENDCLASS To create an object, the following format is used: