Functions, Parameters & Return Values — Lesson 4: Build: Rectangle Area Tool

New skill: Reusable functions and expressions
Previously learned: Unit 02 — data types, variables, expressions

Why this matters

A classroom design app needs a reusable calculation rather than manually recalculating the area of every rectangle.

Study this example

def square_area(side):
    return side * side

print(square_area(5))

The caller provides a value, and the function returns a result. One function works for many different input values.

Before moving on, trace each line of the example by hand. Predict the result before running it in the browser.

Check your understanding

Which parts of the function are general enough to work with a different square size?

Common mistake

Do not hardcode the sample result; the checker will use additional arguments.

Practice: Build: Rectangle Area Tool

Complete calculate_rectangle_area(width, height) to return the area of a rectangle (width * height). It must work with positive and zero dimensions.

Example 1 — Input

calculate_rectangle_area(5, 3)

Output

15

Example 2 — Input

calculate_rectangle_area(0, 10)

Output

0

Example 3 — Input

calculate_rectangle_area(2.5, 4)

Output

10.0

Starter file: main.py

Use Run to experiment and Check to compare against published examples. A passing public example does not automatically establish mastery.

Hint 1 — Identify the key concept

Area is width multiplied by height.

Hint 2 — Find an approach

Don't display output with `print()`.

Hint 3 — Check your answer

Return the calculated value directly or save it to a variable before returning.

Reflection

Write a short explanation of why your code works. What input or change would make it behave differently?