Topic 8: Programming — Part 1

Data Types & Operators

Identifiers, variables, and constants

An identifier is a name given to a variable, constant, or subroutine. Identifiers must start with a letter and should be meaningful so other programmers can understand the code — for example, use TotalMarks rather than X. Meaningful identifiers improve maintainability.

A variable is a named storage location whose value can change while the program runs. Variables are declared with a data type:

DECLARE Score : INTEGER
Score ← 75

A constant is a named value that must stay the same throughout the program. Constants help prevent accidental changes and allow you to update a fixed value once at the top of the code:

CONSTANT MaxAttempts ← 3
CONSTANT PassMark ← 50

Advantages of constants include: values cannot be changed accidentally during execution, and if a fixed value needs updating (such as a tax rate), you change it in one place only.

Diagram comparing variable and constant memory: a variable box whose value can change, and a constant box locked to a fixed value — Diagram 1: A variable stores a value that can be updated; a constant is fixed for the lifetime of the program.

Data types

Every variable must be declared with a data type that defines what kind of value it can store:

Data type	Description	Example
INTEGER	Whole numbers (positive, negative, or zero)	`42`, `-7`, `0`
REAL	Numbers with a fractional part	`3.14`, `98.6`
BOOLEAN	True or false values	`TRUE`, `FALSE`
CHAR	A single character	`'A'`, `'7'`
STRING	A sequence of zero or more characters	`"Hello"`, `""`

Exam Traps

CHAR holds one character in single quotes; STRING holds text in double quotes — "A" is a string, 'A' is a char.

Operators

Arithmetic operators

Arithmetic operators perform calculations on numeric values:

Operator	Meaning	Example
+	Addition	5 + 3 = 8
-	Subtraction	10 - 4 = 6
*	Multiplication	6 * 2 = 12
/	Real division (may produce a decimal result)	10 / 3 = 3.333…
^	Exponent (power)	2 ^ 3 = 8
DIV	Integer division (whole number quotient)	10 DIV 3 = 3
MOD	Remainder after integer division	10 MOD 3 = 1

Relational operators

Relational operators compare two values and return a BOOLEAN result (TRUE or FALSE):

= equal to · <> not equal to · < less than · > greater than · <= less than or equal to · >= greater than or equal to

IF Score >= PassMark THEN
    OUTPUT "Pass"
ENDIF

Logical operators

Logical operators combine BOOLEAN conditions:

AND — both conditions must be true
OR — at least one condition must be true
NOT — reverses a condition (true becomes false, and vice versa)

IF Age >= 18 AND HasTicket = TRUE THEN
    OUTPUT "Entry allowed"
ENDIF

Exam Traps

DIV performs integer division (whole number quotient); / performs real division and may return a decimal — do not confuse them.

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