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Pseudocode Syntax

Comments

// This is a comment

Comments begin with '//' and continue till the end of the line

Variable declaration

DECLARE <name> : <data type>

Available data types:

  • INTEGER
  • REAL
  • BOOLEAN
  • CHAR
  • STRING
  • DATE

Dates are in the format dd/mm/yyyy, literals are used like 14/3/2020

Multiple variables of the same type can be declared with

DECLARE <var1>, <var2>, ... : <data type>

Array declaration:

DECLARE <name> : ARRAY[<lower bound>:<upper bound>] OF <data type>

Note: The bounds are inclusive

Multi Dimensional arrays:

DECLARE <name> : ARRAY[<lb1>:<ub1>, <lb2>:<ub2>, ..., <lbn>:<ubn>] OF <data type>

Accessing array elements

One-dimensional array:

myArray[index]

Multi-dimensional array:

myArray[index1, index2, ..., indexn]

Variable assignment

<variable name> <- <value>

Assigning to an undefined variable will define and initialise it to the value assigned

Assigning to array element

myArray[index] <- <value>
my3dArray[index1, index2, index3] <- <value>

Constants

CONSTANT <name> = <value>

or

CONSTANT <name> <- <value>

Types

Enum definition

TYPE <name> = (State1, State2, State3, ...)

Pointer definition

TYPE <name> = ^<data type>

Composite definition

TYPE <name>
    DECLARE <var1> : <data type 1>
    DECLARE <var2> : <data type 2>
    ...
ENDTYPE

Declaration

DECLARE <variable name> : <type name>

Assignment

// Enum
<enumVar> <- <state>
<enumVar> <- <enumVar> + <integer>

// Pointer
<pointerVar> <- <otherPointerVar>
<pointerVar> <- ^<otherVar>

// Composite
<compositeVar> <- <otherCompositeVar>
<compositeVar>.<member> <- <value>

Accessing pointers

// Access value of ptrVar and store it in var
<var> <- <ptrVar>^

// Assign to variable referenced by pointer
<ptrVar>^ <- <value>

Arithmetic operations

  • + (Addition)
  • - (Subtraction)
  • * (Multiplication)
  • / (Division)
    Result of division operator will always be of type REAL
  • DIV - Integer division
  • MOD - Modulus

Function style syntax may be used for DIV and MOD:

DIV(x, y)
MOD(x, y)

Comparison operators

  • > (Greater than)
  • >= (Greater than or equal to)
  • < (Less than)
  • <= (Less than or equal to)
  • = (Equal to)
  • <> (Not equal to)

Logical operators

  • AND
  • OR
  • NOT

String concatenation

<str1> & <str2>

Selection statements

If statement:

IF <condition> THEN
    ...
ELSE IF <another condition> THEN
    ...
ELSE
    ...
ENDIF
  • ELSE IF and ELSE statements are optional
  • Any number of ELSE IF statements can be used

Case statement:

CASE OF <variable>
    <case 1> : ...
    <case 2> : ...
    ...
    <case n> : ...
    OTHERWISE: ...
ENDCASE
  • OTHERWISE is optional
  • cases may be expressions, e.g (var / 2 + 1)

Loops

While loop:

WHILE <condition> DO
    ...
ENDWHILE

Loops until condition is false

Repeat until loop:

REPEAT
    ...
UNTIL <condition>
  • Loops until the condition is true
  • Condition is checked at the end of an iteration

For loop:

FOR <counterVariable> <- <startValue> TO <stopValue> STEP <stepValue>
    ...
NEXT counterVariable
  • Initialises counterVariable to startValue and loops till it reaches stopValue, incrementing it by stepValue each iteration if provided, otherwise incrementing it by 1
  • STEP <stepValue> and counterVariable after NEXT are optional

Procedures

Procedure with no paramaters:

PROCEDURE <name>
    ...
ENDPROCEDURE

Procedure with parameters:

PROCEDURE <name>([BYREF | BYVAL] <parameterName> : <data type>, <parameter2Name> : <data type>, ...)
    ...
ENDPROCEDURE
  • BYREF - pass parameters by reference
  • BYVAL - pass parameters by value
  • If BYREF or BYVAL is not speified, BYVAL will be used as the default

Calling procedures

No parameters:

CALL <procedureName>

OR

CALL <procedureName>()

With parameters:

CALL <procedureName>(<parameter1>, <parameter2>, ...)

Functions

FUNCTION <name>(...) RETURNS <data type>
    ...
ENDFUNCTION
  • Syntax for function parameters are identical to those of procedures
  • Functions must have a RETURN statement that returns a value of the specified data type

Calling functions

<functionName>(<parameter1>, <parameter2>, ...)

Function calls may be used inside expressions since they return a data type

In-built functions

String functions

// Returns the length of a string
LENGTH(s : STRING) RETURNS INTEGER

// Returns the left n characters of a string
LEFT(s : STRING, n : INTEGER) RETURNS STRING

// Returns the right n characters of a string
RIGHT(s : STRING, n : INTEGER) RETURNS STRING

// Returns a string of length y starting at x
MID(s : STRING, x : INTEGER, y : INTEGER) RETURNS STRING

// Converts all alphabetical characters into uppercase
TO_UPPER(s : STRING) RETURNS STRING

// Converts all alphabetical characters into lowercase
TO_LOWER(s : STRING) RETURNS STRING

// Converts a number into a string
NUM_TO_STR(x : REAL) RETURNS STRING

// Converts a string into a number, returning 0 if the number is invalid
STR_TO_NUM(s : STRING) RETURNS REAL

// Returns whether a string is a valid number
IS_NUM(s : STRING) RETURNS BOOLEAN

Char functions

// Converts a character into lowercase if it is alphabetic
LCASE(c : CHAR) RETURNS CHAR

// Converts a character into uppercase if it is alphabetic
UCASE(c : CHAR) RETURNS CHAR

// Returns the ASCII value of a character
ASC(c : CHAR) RETURNS INTEGER

// Returns the character representation of an ASCII value
CHR(x : INTEGER) RETURNS CHAR

Date functions

// Returns day of month
DAY(Date : DATE) RETURNS INTEGER

// Returns the month
MONTH(Date : DATE) RETURNS INTEGER

// Returns the year
YEAR(Date : DATE) RETURNS INTEGER

// Returns day of week(Starting on Sunday with value 1)
DAYINDEX(Date : DATE) RETURNS INTEGER

// Returns a date with corresponding day, month and year
SETDATE(Day, Month, Year : INTEGER) RETURNS DATE

// Returns current date
TODAY() RETURNS DATE

Time functions

// Returns the unix timestamp(Seconds elapsed since 1st January 1970 UTC)
TIME() RETURNS INTEGER

// Returns the hours on the local clock
HOURS() RETURNS INTEGER

// Returns the minutes on the local clock
MINUTES() RETURNS INTEGER

// Returns the seconds on the local clock
SECONDS() RETURNS INTEGER

Math functions

// Power
POW(x : REAL, y : REAL) RETURNS REAL

// e^x
EXP(x : REAL) RETURNS REAL

// Trigonometric functions
SIN(x : REAL) RETURNS REAL
COS(x : REAL) RETURNS REAL
TAN(x : REAL) RETURNS REAL
ASIN(x : REAL) RETURNS REAL
ACOS(x : REAL) RETURNS REAL
ATAN(x : REAL) RETURNS REAL
ATAN2(y : REAL, x : REAL) RETURNS REAL

// Square root
SQRT(x : REAL) RETURNS REAL

// Logarithm(Base 10)
LOG(x : REAL) RETURNS REAL

// Natural logarithm
LN(x : REAL) RETURNS REAL

Misc functions

// Returns the integer part of a real(floor)
INT(x : REAL) RETURNS INTEGER

// Returns a random number from 0 to x inclusive
RAND(x : INTEGER) RETURNS REAL

// Checks if end of file is reached
EOF(filename : STRING) RETURNS BOOLEAN

I/O

Output to screen

OUTPUT <value>
// or
PRINT <value>

Multiple values can be output at once with

OUTPUT <value1>, <value2>, ...

Get user input

INPUT <variableName>
// or
READ <variableName>

Gets user input and stores it in the given variable

File Handling

Text files

// Open a file
// Modes are READ, WRITE and APPEND
// WRITE mode creates the file if it doesn't exist
OPENFILE <filename> FOR <mode>

// Reads one line form the file into the variable(requires READ mode)
READFILE <filename>, <variable>

// Writes a line with data provided(requires WRITE or APPEND mode)
WRITEFILE <filename>, <data>

// Closes the file
CLOSEFILE <filename>

Random files

// Creates empty file if it does not exist
OPENFILE <filename> FOR RANDOM

// Move file pointer to address
// First address is 1
// Last address is number of records in file + 1 and is write-only to allow appending to the file
SEEK <filename>, <address>

// Read the record at the file pointer into the variable
GETRECORD <filename>, <variable>

// Write the record stored in the variable into the file
PUTRECORD <filename>, <variable>

CLOSEFILE <filename>

Features outside cambridge syntax

  • BREAK - Break out of loops early
  • CONTINUE - Skip to next iteration of loop
  • ELSE IF - Alternative to reduce nesting
  • Alternate method of type conversion(apart from in-built functions): <data type>(<value>). For example: INTEGER("57")
  • Math functions like SIN, EXP
  • Time functions
  • Character escape codes like \n, \t etc.