GCSE Computer Science

Python operators — GCSE Computer Science

Arithmetic operators

• + addition, - subtraction, * multiplication
• / division (always returns a decimal)
• // integer division (rounds down to a whole number)
• % modulo (the remainder after division)
• ** exponentiation (power)

print(17 / 5)    # 3.4
print(17 // 5)   # 3
print(17 % 5)    # 2
print(2 ** 3)    # 8

// and % are the two that catch people out. 17 // 5 asks "how many whole times does 5 go into 17?" — 3. 17 % 5 asks "what's left over?" — 2. Together, they always agree: (17 // 5) * 5 + (17 % 5) comes back to 17.

Comparison operators

== equal to, != not equal to, < less than, > greater than, <= less than or equal to, >= greater than or equal to. Every comparison operator evaluates to True or False.

Logical operators

age = 17
has_id = True

if age >= 18 and has_id:
    print("Entry allowed")

and requires both conditions to be true. or requires at least one. not reverses a boolean. Combining comparison operators with logical operators, as above, is one of the most common patterns in GCSE selection questions.

Assignment operators

total = 0
total += 5    # same as total = total + 5
print(total)  # 5

= assigns a value. += adds to the existing value and reassigns it in one step; -= does the same with subtraction. They're shorthand — total += 5 and total = total + 5 do exactly the same thing.

// and % in pseudocode: DIV and MOD

GCSE pseudocode doesn't use // and % — it uses DIV and MOD instead, and they do exactly the same jobs. 17 DIV 5 is 3. 17 MOD 5 is 2. The mapping between Python and pseudocode here is explicitly tested — know that DIV means // and MOD means %, in both directions.

Operator precedence

Python evaluates ** first, then * / // %, then + -, and comparisons after all of that. Brackets override everything and force a specific order — when in doubt, use them.

result = 2 + 3 * 4
print(result)   # 14, not 20 - multiplication happens before addition

What examiners actually test

Operator questions usually ask you to state the output of an expression using //, %, or a combination of comparison and logical operators, or to convert between Python's // / % and pseudocode's DIV / MOD. Precedence questions — where the order operations happen in changes the answer — come up often enough to be worth memorising the order deliberately, not guessing.