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The current, editable version of this book is available in Wikibooks, the open-content textbooks collection, at
https://en.wikibooks.org/wiki/A_Level_Computer_Science_Programming_Guide
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.
| 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 |
Python has no variable declarations.
| Language | General Usage | Example Usage |
|---|---|---|
| Pseudocode | DECLARE <Identifier> : <Data Type> | DECLARE Weight : INTEGERDECLARE Mass : REALDECLARE Material : STRING |
| VB.NET | Dim<Identifier>As<DataType> | DimWeightAsIntegerDimMassAsDoubleDimMaterialAsString |
Python has no constants.
| Language | General Usage | Example Usage |
|---|---|---|
| Pseudocode | CONSTANT <Identifier> = <Value> | CONSTANT Pi = 3.14CONSTANT e = "2.718"CONSTANT Multiplier = 10 |
| VB.NET | Const<Identifier>As<DataType>=<Value> | ConstPiAsDouble=3.14ConsteAsString="2.17"ConstMultiplierasInteger=10 |
| Language | General Usage | Example Usage |
|---|---|---|
| Pseudocode | <Identifier> ← <Value> | Name ← "Stephen"Age ← 47Weight ← 19.32 |
| VB.NET | <Identifier>=<Value> | Name="Stephen"Age=47Weight=19.32 |
| Python | <Identifier>=<Value> | Name="Stephen"Age=47Weight=19.32 |
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.
| Language | General Usage | Example Usage |
|---|---|---|
| Pseudocode | DECLARE <Identifier> : ARRAY[<Lower Bound>:<Upper Bound>] OF <Data Type> | DECLARE NameList : ARRAY[1:5] OF STRINGDECLARE YearlyRainfall : ARRAY[1900:2100] OF REALDECLARE AgeList : ARRAY[0:40] OF INTEGER |
| VB.NET | Dim<Identifier>(<UpperBound>)As<DataType> | DimNameList(4)AsStringDimYearlyRainfall(200)AsDoubleDimAgeList(40)AsInteger |
| Python | <Identifier>=[] | NameList=[]YearlyRainfall=[]AgeList=[] |
| 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 STRINGDECLARE SudokuGrid : ARRAY[1:9, 1:9] OF INTEGERDECLARE PopulationDensity : ARRAY[1:50, 20:50] OF REAL |
| VB.NET | Dim<Identifier>(<UpperBound>,<UpperBound>)As<DataType> | DimGameArea(31,16)AsStringDimSudokuGrid(8)AsIntegerDimPopulationDensity(49,30)AsDouble |
| Python | <Identifier1>=[]<Identifier2>=[]<Identifier1>.append(<Identifier2>) | Game=[]GameArea=[]GameArea.append(Game)SudokuX=[]SudokuGrid=[]SudokuGrid.append(SudokuX)Longitude=[]PopulationDensity=[]PopulationDensity.append(Longitude) |
| Language | General Usage | Example Usage |
|---|---|---|
| Pseudocode | <Identifier>[<Index>] ← <Value> | NameList[1] ← "Stephen"YearlyRainfall[1985] ← 13.73AgeList[39] ← 17 |
| VB.NET | <Identifier>(<Index>)=<Value> | NameList(0)="Stephen"YearlyRainfall(85)=13.73AgeList(38)=17 |
| Python | <Identifier>.append(<Value>) | NameList.append("Stephen")YearlyRainfall.append(13.73)AgeList.append(17) |
| Language | General Usage | Example Usage |
|---|---|---|
| Pseudocode | <Identifier>[<Index>,<Index>] ← <Value> | GameArea[16, 5] ← "Fire"SudokuGrid[9, 3] ← 7PopulationDensity[14, 32] ← 242.023 |
| VB.NET | <Identifier>(<Index>,<Index>)=<Value> | GameArea(15,5)="Fire"SudokuGrid(8,2)=7PopulationDensity(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) |
Warning: Display title "User-Defined Data Types" overrides earlier display title "Variables, Constants and 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><Value1>=<Reference><Value2>=<Reference><Value3>=<Reference>....EndEnum | EnumSeasonSummer=1Autumn=2Winter=3Spring=4EndEnumEnumSpiceIntensityNone=0Mild=1Medium=2Hot=3Extreme=4EndEnum |
| Language | General Usage | Example Usage |
|---|---|---|
| Pseudocode | DECLARE <Identifier> : <Data Type><Identifier> ← <Value> | DECLARE Seasons : SeasonSeasons ← AutumnDECLARE CompassPointer : DirectionCompassPointer ← NorthDECLARE SpicePreference : SpiceIntensitySpicePreference ← Extreme |
| VB.NET | Dim<Identifier>As<DataType><Integer Variable>=<Identifier>.<Value> | DimSeasonsAsSeasonSeasonCounter=Seasons.AutumnDimCompassPointerAsDirectionCurrentDirection=CompassPointer.NorthDimSpicePreferenceAsSpiceIntensitySpiceCounter=SpicePreference.Extreme |
There is no VB.Net equivalent for a Pointer Data Type.
| Language | General Usage | Example Usage |
|---|---|---|
| Pseudocode | TYPE <Pointer> = ^<Type Name> | Type AddPointer = ^INTEGERType NextLocation = ^STRINGType Pass = ^REAL |
| 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 : SpiceIntensityEND TYPE |
| VB.NET | Structure<Identifier>Dim<Identifier>As<Datatype>Dim<Identifier>As<Datatype>...EndStructure | StructurePersonDimNameAsStringDimBirthdayAsDateDimWeightAsDoubleDimAddressAsStringDimSpicePreferenceAsSpiceIntensityEndStructure |
Warning: Display title "Common Operations" overrides earlier display title "User-Defined Data Types".
| Language | General Usage | Example Usage |
|---|---|---|
| Pseudocode | INPUT <Identifier> | Input AnswerInput AgeInput DistanceTravelled |
| VB.NET | <Identifier>=Console.Readline()Dim<Identifier>As<DataType>=Console.ReadLine() | Answer=Console.ReadLine()DimAgeAsInteger=Console.ReadLine()DistanceTravelled=Console.ReadLine() |
| 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 |
| Language | General Usage | Example Usage |
|---|---|---|
| Pseudocode | ||
| VB.NET |
| Language | General Usage | Example Usage |
|---|---|---|
| Pseudocode | RANDOMBETWEEN(<Minimum>, <Maximum>) INTEGER between the Minimum and Maximum.RND() REAL number between0 and1. | DECLARE Random : INTEGERRandom = RANDOMBETWEEN(10, 17)DECLARE Random : REALRandom = RND() |
| VB.NET | <Variable>=<Minimum>+Rnd()*(<Maximum>-<Minimum>) Rnd() REAL number between0 and1. | DimRandomAsIntegerRandom=RANDOMBETWEEN(10,17)Random=10+Rnd()*(17-10)DimRandomAsDoubleRandom=Rnd() |
Warning: Display title "Selection" overrides earlier display title "Common Operations".
| Language | General Usage | Example Usage |
|---|---|---|
| Pseudocode | / If...Then StatementIF <Condition> THEN <Statements>ENDIF/ If...Then...Else StatementIF <Condition> THEN <Statements> ELSE <Statements>ENDIF/ ElseIf StatementIF <Condition> THEN <Statements>ELSEIF <Condition> THEN <Statements> ELSE <Statements>ENDIF | / If...Then StatementIF Age < 16 THEN CanDrive ← FALSEENDIF/ If...Then...Else StatementIF IsGreen THEN OUTPUT "Green" ELSE OUTPUT "Blue"ENDIF/ ElseIf StatementIF Score > 1000 THEN Multiplier ← 10ELSEIF Score < 500 THEN Multiplier ← 0 ELSE Multiplier ← 5ENDIF |
| VB.NET | 'If...Then StatementIf<Condition>Then<Statements>EndIf'If...Then...Else StatementIf<Condition>Then<Statements>Else<Statements>EndIf'Else If StatementIf<Condition>Then<Statements>ElseIf<Condition>Then<Statements>Else<Statements>EndIF | 'If...Then StatementIfAge<16ThenCanDrive=FalseEndIf'If...Then...Else StatementIfIsGreenThenConsole.WriteLine("Green")ElseConsole.WriteLine("Blue")EndIf'Else If StatementIfScore>1000ThenMultiplier=10ElseIfScore<500ThenMultiplier=0ElseMultiplier=5EndIf |
| Language | General Usage | Example Usage |
|---|---|---|
| Pseudocode | IF <Condition> THEN IF <Condition> THEN <Statements> ENDIFENDIF | IF Found = False THEN IF Searching = false THEN CALL Search() ENDIFENDIFIF 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>ThenIf<Condition>Then<Statements>EndIfEndIf | IfFound=FalseThenIfSearching=falseThenSearch()EndIfEndIfIfAge>=16ThenIfPassedLicenceTest=TrueThenGenerateLicence()ElseIfTakenTest=FalseThenConsole.WriteLine("You need to take the test to get your licence")ElseConsole.WriteLine("You Failed Your Test")Console.WriteLine("You need to pass the test to get your licence")EndIfElseConsole.WriteLine("Ineligible for Licence")EndIf |
| Language | General Usage | Example Usage |
|---|---|---|
| Pseudocode | CASE OF <identifier> <value 1> : <statement> <value 2> : <statement> ...ENDCASECASE OF <identifier> <value 1> : <statement> <value 2> : <statement> ... OTHERWISE <statement>ENDCASE | / If...Then StatementIF Age < 16 THEN CanDrive ← FALSEENDIF/ If...Then...Else StatementIF IsGreen THEN OUTPUT "Green" ELSE OUTPUT "Blue"ENDIF/ ElseIf StatementIF Score > 1000 THEN Multiplier ← 10ELSEIF Score < 500 THEN Multiplier ← 0 ELSE Multiplier ← 5ENDIF |
| VB.NET | 'If...Then StatementIf<Condition>Then<Statements>EndIf'If...Then...Else StatementIf<Condition>Then<Statements>Else<Statements>EndIf'Else If StatementIf<Condition>Then<Statements>ElseIf<Condition>Then<Statements>Else<Statements>EndIF | 'If...Then StatementIfAge<16ThenCanDrive=FalseEndIf'If...Then...Else StatementIfIsGreenThenConsole.WriteLine("Green")ElseConsole.WriteLine("Blue")EndIf'Else If StatementIfScore>1000ThenMultiplier=10ElseIfScore<500ThenMultiplier=0ElseMultiplier=5EndIf |
Warning: Display title "File Handling" overrides earlier display title "Selection".
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.
| Language | General Usage | Example Usage |
|---|---|---|
| Pseudocode | OPENFILE <File Identifier> FOR <File Mode> | OPENFILE Beans.txt FOR APPENDOPENFILE Styles.css FOR READOPENFILE Names.tmp FOR WRITE |
| VB.NET | FileOpen(<FileNumber>],<FileIdentifier>,OpenMode.<FileMode>) | FileOpen(17,“Beans.txt”,OpenMode.Append)FileOpen(FileNumber,“Styles.css”,OpenMode.Input)FileOpen(NamesFile,“Names.tmp”,OpenMode.Output) |
InVB.NET you can use theFreeFile() function to automatically obtain an unused file number, avoiding any problems that could occur if accidentally using the same number for two files.
DimFileNumberAsInteger=FreeFile()
It is good practice toalways keep track of your file numbers, as it will help reduce bugs (aka forgetting or using the wrong file number), remove anyMagic Numbers and make the code easier to read and understand.
| File Mode Identifiers | Description | |
|---|---|---|
| Pseudocode | VB.NET | |
APPEND | OpenMode.Append | Used whenWriting data to the file. If the file already exists, the new data will beadded to the file after any existing data. |
READ | OpenMode.Input | Used whenReading data from the file. |
Write | OpenMode.Output | Used whenWriting data to the file. If the file already exists, the file will bedeleted and anew file will be created with the new data. |
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 stringsREADFILE Styles.css, NextLineREADFILE TransactionHistory.txt, TransactionREADFILE Address.db, CurrentAddressWRITEFILE <File identifier>, <Variable> |
| VB.NET | <Identifier>=LineInput(<FileIdentifier>) 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 typeSTRING. This command reads the text file line by line.
TheEOF() function can be used inPseudocode andVB.NET to determine whether the file pointer is at the end of the file. It returns aBoolean Value, and can be useful when implementing loops.
EOF(<File Identifier>)
| Pseudocode | VB.NET |
|---|---|
EOF(file.txt) | EOF(FileNumber) |
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, BeanDataWRITEFILE Names.tmp, CurrentUserWRITEFILE Recipes.db, NewRecipe |
| VB.NET | PrintLine(<FileIdentifier>,<Identifier>) 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 typeSTRING.
| Language | General Usage | Example Usage |
|---|---|---|
| Pseudocode | CLOSEFILE <File identifier> | CLOSEFILE Beans.txtCLOSEFILE Styles.cssCLOSEFILE Names.tmp |
| VB.NET | FileClose(<FileIdentifier>) File Identifer is the file number used identify the file when it was opened. | FileClose(17)FileClose(FileNumber)FileClose(NamesFile) |
You shouldalways 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.