Operators

OCR J277 Paper 2 expects you to know the symbol, name and effect of every operator on the spec. Mistakes with MOD, DIV, integer division and string comparison appear every year.

Arithmetic operators

Symbol	Meaning	Example	Result
+	Addition	7 + 3	10
−	Subtraction	7 − 3	4
*	Multiplication	7 * 3	21
/	Division (real result)	7 / 2	3.5
MOD	Modulus — remainder of integer division	7 MOD 3	1
DIV	Integer division — quotient discarding remainder	7 DIV 3	2
^	Exponentiation (to the power of)	2 ^ 3	8

Common uses of MOD and DIV

• isEven(x) — true if x MOD 2 = 0.
• Convert seconds to minutes and seconds — minutes = totalSeconds DIV 60; seconds = totalSeconds MOD 60.
• Last digit of an integer — n MOD 10.

Comparison (relational) operators

Symbol	Meaning
=	Equal to
≠ (or <>)	Not equal to
<	Less than
≤	Less than or equal to
>	Greater than
≥	Greater than or equal to

Comparison operators always evaluate to a Boolean (TRUE / FALSE). They work on numbers and (in most languages) strings, where the comparison is alphabetical/lexicographic.

Boolean (logical) operators

Operator	Effect
AND	TRUE only if both operands are TRUE
OR	TRUE if either operand (or both) is TRUE
NOT	Reverses the value (TRUE ↔ FALSE)

Order of evaluation

In an expression, the order is usually:

1. Brackets
2. ^ (exponent)
3. *, /, DIV, MOD
4. +, -
5. Comparison
6. NOT, AND, OR (NOT first, then AND, then OR)

Use brackets when in doubt.

Common OCR exam mistakes

• Using / when DIV is needed (or vice-versa) — / returns a real, DIV returns an integer.
• Saying 7 MOD 3 = 2 — it is 1 (the remainder, not the quotient).
• Mixing up ≤ and < (boundary errors), or ≥ and >.
• Forgetting NOT has higher precedence than AND/OR.
• Using = for assignment in pseudocode where OCR uses ← — be careful in code-reading questions.