Part 2: Core Programming Concepts

2. Operators & Expressions

Making the computer calculate and decide

An operator is a symbol that performs an operation on one or more values, called operands. When you combine values and operators you form an expression — something the computer evaluates down to a single result. 3 + 4 is an expression that evaluates to 7; price * quantity is an expression whose result depends on the current values of those variables.

Arithmetic operators

These do ordinary maths. Note the two "division-like" operators many languages provide: regular division and remainder (modulo), which gives what is left over.

Operator	Meaning	Example	Result
+	Addition	7 + 2	9
-	Subtraction	7 - 2	5
*	Multiplication	7 * 2	14
/	Division	7 / 2	3.5
%	Modulo (remainder)	7 % 2	1
**	Exponent (power)	7 ** 2	49

Modulo is more useful than it looks: n % 2 == 0 tests whether n is even, and modulo is how you wrap around clock faces, grids and buffers.

Comparison operators

Comparison operators ask a question about two values and always produce a boolean (true or false): == (equal), != (not equal), <, >, <=, >=. The single most common beginner bug is writing = (assignment) where you meant == (comparison).

age = 20
age == 18   # False  (is it equal to 18?)
age >= 18   # True   (18 or more?)
age != 18   # True   (not equal to 18?)

Logical operators

Logical operators combine boolean values so you can express compound conditions: AND is true only when both sides are true; OR is true when at least one side is true; NOT flips a value. The full behaviour is captured in a truth table:

A	B	A AND B	A OR B	NOT A
True	True	True	True	False
True	False	False	True	False
False	True	False	True	True
False	False	False	False	True

age = 25
has_ticket = True
age >= 18 and has_ticket   # True  — both conditions hold

Assignment operators

Besides plain =, most languages offer compound assignment that updates a variable in place: x += 3 means x = x + 3. The family includes -=, *=, /= and more. They are shorthand, not new powers.

Operator precedence

When an expression mixes operators, the computer follows precedence rules — essentially the maths "BODMAS/PEMDAS" order. Multiplication and division happen before addition and subtraction, and comparisons happen before logical operators. When in doubt, add parentheses: they are free, and they make intent unmistakable.

2 + 3 * 4        # 14, not 20 — * runs first
(2 + 3) * 4      # 20 — parentheses force the addition first
age >= 18 and age < 65   # comparisons evaluate before 'and'

Key idea: operators turn values into new values; an expression is any combination that evaluates to a single result, governed by precedence.