File Handling

A Level Computer Science Programming Guide

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Introduction

This Wikibook is not designed to teach you how to program, but rather to help you to remember and easily translate your code to the different languages.

All Pseudocode in this guide is based on various Cambridge Mark Schemes and Help Guides, so it is as accurate as possible.

When complete, the High-Level languages covered in this guide will be those that are set in the Cambridge syllabus; VB.Net, Python and Pascal/Delphi.

Variables, Constants and Data Types

Data types and their usage

Pseudocode

Data Type	Description	Usage	Example
INTEGER	A whole number	Uses the normal denary system	123, -123, 0
REAL	Any number that has fractional parts/decimals	Written with at least one digit either side of a decimal point	12.4, 3.0, -17.34
CHAR	A single character	A single character enclosed between single quotation marks	'a', '@', '5'
STRING	A series of zero or more characters	No, or a series of characters enclosed between double quotation marks	"banana", "Q173hf", "John Doe"
BOOLEAN	A logical Expression	True or False	TRUE, FALSE
DATE	Any valid date	Use the format: dd/mm/yyyy If a different format must be used, use a comment to explain your decision.	21/10/2015, 03/07/1985, 12/11/1955

Variable Declarations

Python has no variable declarations.

Language	General Usage	Example Usage
Pseudocode	DECLARE <Identifier> : <Data Type>	DECLARE Weight : INTEGER DECLARE Mass : REAL DECLARE Material : STRING
VB.NET	Dim <Identifier> As <Data Type>	Dim Weight As Integer Dim Mass As Double Dim Material As String

Constants

Python has no constants.

Language	General Usage	Example Usage
Pseudocode	CONSTANT <Identifier> = <Value>	CONSTANT Pi = 3.14 CONSTANT e = "2.718" CONSTANT Multiplier = 10
VB.NET	Const <Identifier> As <Data Type> = <Value>	Const Pi As Double = 3.14 Const e As String = "2.17" Const Multiplier as Integer = 10

Assignments

Language	General Usage	Example Usage
Pseudocode	<Identifier> ← <Value>	Name ← "Stephen" Age ← 47 Weight ← 19.32
VB.NET	<Identifier> = <Value>	Name = "Stephen" Age = 47 Weight = 19.32
Python	<Identifier> = <Value>	Name = "Stephen" Age = 47 Weight = 19.32

Arrays

Declaring Arrays

In Pseudocode, Arrays all have declarable Upper and Lower bounds.

In VB.NET, Arrays all have declarable Upper Bounds, but Lower Bounds are always 0.

One Dimensional Arrays

Language	General Usage	Example Usage
Pseudocode	DECLARE <Identifier> : ARRAY[<Lower Bound>:<Upper Bound>] OF <Data Type>	DECLARE NameList : ARRAY[1:5] OF STRING DECLARE YearlyRainfall : ARRAY[1900:2100] OF REAL DECLARE AgeList : ARRAY[0:40] OF INTEGER
VB.NET	Dim <Identifier>(<Upper Bound>) As <Data Type>	Dim NameList(4) As String Dim YearlyRainfall(200) As Double Dim AgeList(40) As Integer
Python	<Identifier> = []	NameList = [] YearlyRainfall = [] AgeList = []

Two Dimensional Arrays

Language	General Usage	Example Usage
Pseudocode	DECLARE <Identifier> : ARRAY[<Lower Bound>:<Upper Bound>, <Lower Bound>:<Upper Bound>] OF <Data Type>	DECLARE GameArea : ARRAY[1:32, 0:16] OF STRING DECLARE SudokuGrid : ARRAY[1:9, 1:9] OF INTEGER DECLARE PopulationDensity : ARRAY[1:50, 20:50] OF REAL
VB.NET	Dim <Identifier>(<Upper Bound>, <Upper Bound>) As <Data Type>	Dim GameArea(31, 16) As String Dim SudokuGrid(8) As Integer Dim PopulationDensity(49,30) As Double
Python	<Identifier1> = [] <Identifier2> = [] <Identifier1>.append(<Identifier2>)	Game = [] GameArea = [] GameArea.append(Game) SudokuX = [] SudokuGrid = [] SudokuGrid.append(SudokuX) Longitude = [] PopulationDensity = [] PopulationDensity.append(Longitude)

Using Arrays

One Dimensional Arrays

Language	General Usage	Example Usage
Pseudocode	<Identifier>[<Index>] ← <Value>	NameList[1] ← "Stephen" YearlyRainfall[1985] ← 13.73 AgeList[39] ← 17
VB.NET	<Identifier>(<Index>) = <Value>	NameList(0) = "Stephen" YearlyRainfall(85) = 13.73 AgeList(38) = 17
Python	<Identifier>.append(<Value>)	NameList.append("Stephen") YearlyRainfall.append(13.73) AgeList.append(17)

Two Dimensional Arrays

Language	General Usage	Example Usage
Pseudocode	<Identifier>[<Index>,<Index>] ← <Value>	GameArea[16, 5] ← "Fire" SudokuGrid[9, 3] ← 7 PopulationDensity[14, 32] ← 242.023
VB.NET	<Identifier>(<Index>,<Index>) = <Value>	GameArea(15, 5) = "Fire" SudokuGrid(8, 2) = 7 PopulationDensity(13, 12) = 242.023
Python	<Identifier1> = [] <Identifier2> = [] <Identifier1>.append(<Identifier2>)	Game.append("Fire") GameArea.append(Game) SudokoX.append(7) SudokuGrid.append(SudokuX) Longitude.append(242.023) PopulationDensity.append(Longitude)

User-Defined Data Types

Enumerated Data Types

Declaring Enumerated Data Types

Language	General Usage	Example Usage
Pseudocode	TYPE <Identifier> = (<Value 1>, <Value 2>, <Value 3>, ...)	TYPE Season = (Summer, Autumn, Winter, Spring) TYPE Direction = (North, North_East, East, South_East, South, South_West, West, North_West) TYPE SpiceIntensity = (No_Preference ,None, Mild, Medium, Hot, Extreme)
VB.NET	Enum <Identifier> <Value 1> = <Reference> <Value 2> = <Reference> <Value 3> = <Reference> .... End Enum	Enum Season Summer = 1 Autumn = 2 Winter = 3 Spring = 4 End Enum Enum SpiceIntensity None = 0 Mild = 1 Medium = 2 Hot = 3 Extreme = 4 End Enum

Using Enumerated Data Types

Language	General Usage	Example Usage
Pseudocode	DECLARE <Identifier> : <Data Type> <Identifier> ← <Value>	DECLARE Seasons : Season Seasons ← Autumn DECLARE CompassPointer : Direction CompassPointer ← North DECLARE SpicePreference : SpiceIntensity SpicePreference ← Extreme
VB.NET	Dim <Identifier> As <Data Type> <Integer Variable> = <Identifier>.<Value>	Dim Seasons As Season SeasonCounter = Seasons.Autumn Dim CompassPointer As Direction CurrentDirection = CompassPointer.North Dim SpicePreference As SpiceIntensity SpiceCounter = SpicePreference.Extreme

Pointer Data Types

There is no VB.Net equivalent for a Pointer Data Type.

Language	General Usage	Example Usage
Pseudocode	TYPE <Pointer> = ^<Type Name>	Type AddPointer = ^INTEGER Type NextLocation = ^STRING Type Pass = ^REAL

Record Data Types

Language	General Usage	Example Usage
Pseudocode	TYPE <Identifier> DECLARE <Identifier> : <Data Type> DECLARE <Identifier> : <Data Type> ... END TYPE	TYPE Person DECLARE Name : STRING DECLARE Birthday : DATE DECLARE Weight : REAL DECLARE Address : STRING DECLARE SpicePreference : SpiceIntensity END TYPE
VB.NET	Structure <Identifier> Dim <Identifier> As <Datatype> Dim <Identifier> As <Datatype> ... End Structure	Structure Person Dim Name As String Dim Birthday As Date Dim Weight As Double Dim Address As String Dim SpicePreference As SpiceIntensity End Structure

Common Operations

Input And Output

Language	General Usage	Example Usage
Pseudocode	INPUT <Identifier>	Input Answer Input Age Input DistanceTravelled
VB.NET	<Identifier> = Console.Readline() Dim <Identifier> As <Data Type> = Console.ReadLine()	Answer = Console.ReadLine() Dim Age As Integer = Console.ReadLine() DistanceTravelled = Console.ReadLine()

Arithmetic, Relational and Logic Operators

Language	Arithmetic Operators				Integer Division		Relational Operators						Logic Operators
	Addition	Subtraction	Multiplication	Division	Modulus	Division	Greater Than	Less Than	Greater Than or Equal to	Less Than or Equal to	Equal To	Not Equal To	AND	OR	NOT
Pseudocode	+	-	*	/	MOD	DIV	>	<	>=	<=	=	<>	AND	OR	NOT
VB.NET	+	-	*	/	MOD	\	>	<	>=	<=	=	<>	AND	OR	NOT

String Operators

Language	General Usage	Example Usage
Pseudocode
VB.NET

Random Number Generation

Language	General Usage	Example Usage
Pseudocode	RANDOMBETWEEN(<Minimum>, <Maximum>) Generates a random INTEGER between the Minimum and Maximum. RND() Generates a random REAL number between 0 and 1.	DECLARE Random : INTEGER Random = RANDOMBETWEEN(10, 17) DECLARE Random : REAL Random = RND()
VB.NET	<Variable> = <Minimum> + Rnd() * (<Maximum> - <Minimum>) Generates a random INTEGER between the Minimum and Maximum. Rnd() Generates a random REAL number between 0 and 1.	Dim Random As Integer Random = RANDOMBETWEEN(10, 17) Random = 10 + Rnd() * (17 - 10) Dim Random As Double Random = Rnd()

Selection

IF Statements

Language	General Usage	Example Usage
Pseudocode	/ If...Then Statement IF <Condition> THEN <Statements> ENDIF / If...Then...Else Statement IF <Condition> THEN <Statements> ELSE <Statements> ENDIF / ElseIf Statement IF <Condition> THEN <Statements> ELSEIF <Condition> THEN <Statements> ELSE <Statements> ENDIF	/ If...Then Statement IF Age < 16 THEN CanDrive ← FALSE ENDIF / If...Then...Else Statement IF IsGreen THEN OUTPUT "Green" ELSE OUTPUT "Blue" ENDIF / ElseIf Statement IF Score > 1000 THEN Multiplier ← 10 ELSEIF Score < 500 THEN Multiplier ← 0 ELSE Multiplier ← 5 ENDIF
VB.NET	'If...Then Statement If <Condition> Then <Statements> End If 'If...Then...Else Statement If <Condition> Then <Statements> Else <Statements> End If 'Else If Statement If <Condition> Then <Statements> Else If <Condition> Then <Statements> Else <Statements> End IF	'If...Then Statement If Age < 16 Then CanDrive = False End If 'If...Then...Else Statement If IsGreen Then Console.WriteLine("Green") Else Console.WriteLine("Blue") End If 'Else If Statement If Score > 1000 Then Multiplier = 10 Else If Score < 500 Then Multiplier = 0 Else Multiplier = 5 End If

Nested IF Statements

Language	General Usage	Example Usage
Pseudocode	IF <Condition> THEN IF <Condition> THEN <Statements> ENDIF ENDIF	IF Found = False THEN IF Searching = false THEN CALL Search() ENDIF ENDIF IF Age >= 16 THEN IF PassedLicenceTest = True THEN CALL GenerateLicence() ELSEIF TakenTest = False THEN OUTPUT "You need to take the test to get your licence" ELSE OUTPUT "You Failed Your Test" OUTPUT "You need to pass the test to get your licence" ENDIF ELSE OUTPUT "Ineligible for Licence" ENDIF
VB.NET	If <Condition> Then If <Condition> Then <Statements> End If End If	If Found = False Then If Searching = false Then Search() End If End If If Age >= 16 Then If PassedLicenceTest = True Then GenerateLicence() Else If TakenTest = False Then Console.WriteLine("You need to take the test to get your licence") Else Console.WriteLine("You Failed Your Test") Console.WriteLine("You need to pass the test to get your licence") End If Else Console.WriteLine("Ineligible for Licence") End If

CASE Statements

Language	General Usage	Example Usage
Pseudocode	CASE OF <identifier> <value 1> : <statement> <value 2> : <statement> ... ENDCASE CASE OF <identifier> <value 1> : <statement> <value 2> : <statement> ... OTHERWISE <statement> ENDCASE	/ If...Then Statement IF Age < 16 THEN CanDrive ← FALSE ENDIF / If...Then...Else Statement IF IsGreen THEN OUTPUT "Green" ELSE OUTPUT "Blue" ENDIF / ElseIf Statement IF Score > 1000 THEN Multiplier ← 10 ELSEIF Score < 500 THEN Multiplier ← 0 ELSE Multiplier ← 5 ENDIF
VB.NET	'If...Then Statement If <Condition> Then <Statements> End If 'If...Then...Else Statement If <Condition> Then <Statements> Else <Statements> End If 'Else If Statement If <Condition> Then <Statements> Else If <Condition> Then <Statements> Else <Statements> End IF	'If...Then Statement If Age < 16 Then CanDrive = False End If 'If...Then...Else Statement If IsGreen Then Console.WriteLine("Green") Else Console.WriteLine("Blue") End If 'Else If Statement If Score > 1000 Then Multiplier = 10 Else If Score < 500 Then Multiplier = 0 Else Multiplier = 5 End If

File Handling

Note for VB.NET users:

While the methods used here are still valid, they are generally not used. They have been included in this guide as they are more similar to the Pseudocode file management, hopefully making them easier to understand. Even though it is not practice to use them, they should still be acceptable in an exam.

Handling Text Files

Opening Text Files

Language	General Usage	Example Usage
Pseudocode	OPENFILE <File Identifier> FOR <File Mode>	OPENFILE Beans.txt FOR APPEND OPENFILE Styles.css FOR READ OPENFILE Names.tmp FOR WRITE
VB.NET	FileOpen(<File Number>], <File Identifier>, OpenMode.<File Mode>)	FileOpen(17, “Beans.txt”, OpenMode.Append) FileOpen(FileNumber, “Styles.css”, OpenMode.Input) FileOpen(NamesFile, “Names.tmp”, OpenMode.Output)

In VB.NET you can use the FreeFile() function to automatically obtain an unused file number, avoiding any problems that could occur if accidentally using the same number for two files.

Dim FileNumber As Integer = FreeFile()

It is good practice to always keep track of your file numbers, as it will help reduce bugs (aka forgetting or using the wrong file number), remove any Magic Numbers and make the code easier to read and understand.

File Mode Usage

File Mode Identifiers		Description
Pseudocode	VB.NET
APPEND	OpenMode.Append	Used when Writing data to the file. If the file already exists, the new data will be added to the file after any existing data.
READ	OpenMode.Input	Used when Reading data from the file.
Write	OpenMode.Output	Used when Writing data to the file. If the file already exists, the file will be deleted and a new file will be created with the new data.

Reading From Text Files

Once a file is opened in 'Read' mode, you can use the following commands to read the data from the files.

Language	General Usage	Example Usage
Pseudocode	READFILE <File Identifier>, <Identifier>	/Datatypes declared as strings READFILE Styles.css, NextLine READFILE TransactionHistory.txt, Transaction READFILE Address.db, CurrentAddress WRITEFILE <File identifier>, <Variable>
VB.NET	<Identifier> = LineInput(<File Identifier>) The File Identifer is the file number used identify the file when it was opened.	NextLine = LineInput(StylesFileNumber) Transaction = LineInput(TransactionHistoryFileNumber) CurrentAddress = LineInput(AddressFileNumber)

The Variable should be of data type STRING. This command reads the text file line by line.

The EOF() function can be used in Pseudocode and VB.NET to determine whether the file pointer is at the end of the file. It returns a Boolean Value, and can be useful when implementing loops.

EOF(<File Identifier>)

Pseudocode	VB.NET
EOF(file.txt)	EOF(FileNumber)

Writing To Text Files

Once a file is opened in 'Write' or 'Append' mode, you can use the following commands to write the data to the files.

Language	General Usage	Example Usage
Pseudocode	READFILE <File Identifier>, <Identifier>	WRITEFILE Beans.txt, BeanData WRITEFILE Names.tmp, CurrentUser WRITEFILE Recipes.db, NewRecipe
VB.NET	PrintLine(<File Identifier>, <Identifier>) The File Identifer is the file number used identify the file when it was opened.	PrintLine("Beans.txt", BeanData) PrintLine("Name.tmp", CurrentUser) PrintLine("Recipes.db" NewRecipe)

The Variable should be of data type STRING.

Closing Text Files

Language	General Usage	Example Usage
Pseudocode	CLOSEFILE <File identifier>	CLOSEFILE Beans.txt CLOSEFILE Styles.css CLOSEFILE Names.tmp
VB.NET	FileClose(<File Identifier>) The File Identifer is the file number used identify the file when it was opened.	FileClose(17) FileClose(FileNumber) FileClose(NamesFile)

You should always remember to close your files. Failure to do so can result in major problems later on when any program tries to open the file, or the program tries to open or edit a different file with the same identifier.

Algorithms

Sorting

• Bubble Sort
• Insertion Sort

Searching

• Binary Sort

Listing

• Stacks
• Queues
• Linked Lists
• Binary Trees
• Hash Tables