Programming

• Declare constants with CONSTANT (literal values only) and variables with DECLARE Name : TYPE; assign with ←.
• Data types: INTEGER, REAL, CHAR, STRING, BOOLEAN, DATE. A REAL literal always has a digit either side of the point (4.0, 0.5).
• Arithmetic: + − * /, DIV (quotient) and MOD (remainder). "/" always gives a REAL.
• Built-in functions you are given in the insert: LEFT, RIGHT, MID, LENGTH, TO_UPPER, TO_LOWER, NUM_TO_STR, STR_TO_NUM, IS_NUM, ASC, CHR, INT, RAND, the date functions and EOF.
• Selection: IF … THEN … ELSE … ENDIF (nested where needed) and CASE OF … OTHERWISE … ENDCASE, including ranges such as 70 TO 100.
• Iteration: count-controlled FOR … NEXT, post-condition REPEAT … UNTIL (runs at least once), pre-condition WHILE … ENDWHILE (may run zero times).
• Procedures are called with CALL; functions return one value and are used inside an expression. Parameters are passed BYVAL (default) or BYREF.
• Know the vocabulary: header, interface, parameter, argument, return value, local and global variables.

Constants, variables, assignment, input and output

Every Paper 2 algorithm starts with the data it needs. A variable holds a value that can change while the program runs; a constant is fixed when the program is written. Declare both at the top so the reader (and the examiner) can see the types.

CONSTANT MaxMark = 100
CONSTANT PassText = "Pass"
DECLARE StudentName : STRING
DECLARE Mark : INTEGER
DECLARE Percentage : REAL
DECLARE Passed : BOOLEAN

INPUT StudentName
INPUT Mark
Percentage ← (Mark / MaxMark) * 100
Passed ← Percentage >= 50
OUTPUT StudentName, " scored ", Percentage, "%"

A constant may only be given a literal: CONSTANT Limit = MaxMark * 2 is not allowed. Constants make code easier to read and to update, because the value is changed in one place.

Operators

Built-in functions and library routines

You never have to memorise exact string functions: the exam insert lists them. What you must do is use them correctly: count positions from 1, and give MID a start and a length, not a start and an end.