Functions in HKDSE ICT: What You Must Know

Why Functions Matter in HKDSE

Functions appear in over 90% of HKDSE ICT Paper 1 questions. Paper 1B almost always has a multi-part question requiring you to define and call functions. Master this topic and you unlock 15-20 marks.

Anatomy of a Function

def function_name(parameter1, parameter2):
    # code here
    return value

• def — the keyword that defines a function
• function_name — your chosen name (snake_case by convention)
• Parameters — inputs the function receives
• return — the value sent back to the caller

Simple Example

def square(n):
    return n * n

print(square(5))   # 25
print(square(10))  # 100

Multiple Parameters

def add(a, b):
    return a + b

def bmi(weight, height):
    return weight / (height ** 2)

print(add(3, 4))        # 7
print(bmi(60, 1.70))    # 20.76...

Default Parameters

def greet(name, greeting="Hello"):
    return f"{greeting}, {name}!"

print(greet("Chan"))               # "Hello, Chan!"
print(greet("Lee", "Good morning")) # "Good morning, Lee!"

Multiple Return Values (Common in HKDSE)

def min_max(lst):
    return min(lst), max(lst)

lowest, highest = min_max([3, 1, 4, 1, 5, 9])
print(lowest, highest)   # 1 9

Functions Without Return

A function without return returns None. Common for functions that just print:

def print_header():
    print("=" * 30)
    print("STUDENT REPORT")
    print("=" * 30)

print_header()

Scope: The Trickiest Topic

Variables inside a function are local — they don't exist outside.

def compute():
    x = 10        # local to compute()
    return x

compute()
print(x)   # NameError — x doesn't exist here

Global Variables

total = 0

def add_score(n):
    global total   # needed to modify
    total += n

add_score(5)
add_score(3)
print(total)   # 8

Common HKDSE Question Pattern

"Write a function calculate_grade(score) that returns the grade letter based on the following scheme..."

def calculate_grade(score):
    if score >= 80: return 'A'
    elif score >= 65: return 'B'
    elif score >= 50: return 'C'
    elif score >= 35: return 'D'
    else: return 'F'

# Use in main program
scores = [78, 92, 45, 67]
for s in scores:
    print(f"{s}: {calculate_grade(s)}")

Functions Calling Other Functions

Paper 1B often requires function composition:

def is_vowel(char):
    return char.lower() in 'aeiou'

def count_vowels(text):
    count = 0
    for char in text:
        if is_vowel(char):
            count += 1
    return count

print(count_vowels("HKDSE ICT"))  # 2

Testing Checklist

• Did I use def to define the function?
• Are parameters in the correct order?
• Does every code path have a return (if needed)?
• Am I actually calling the function somewhere?
• Are variable names matching what the question specifies?