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S1Q3 · Double if Even, Else Square

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Function: double_if_even_else_square(n) -> int

Core idea: Check parity with n % 2 == 0, then return 2*n or n**2.

def double_if_even_else_square(n):
    return 2 * n if n % 2 == 0 else n ** 2

Key rules: - Even (n % 2 == 0): return 2 * n - Odd: return n ** 2 - Works for negative integers and zero (0 is even)

Problem Statement

Problem

Write a function double_if_even_else_square(n) that doubles n if it is even, or returns n squared if it is odd.

Examples:

Call 
double_if_even_else_square(8)
Output 
16
Call 
double_if_even_else_square(9)
Output 
81

Understanding the problem

n Even? Operation Result
8 ✅ 2 × 8 16
9 ✗ 9² 81
0 ✅ 2 × 0 0
-4 ✅ 2 × -4 -8
-3 ✗ (-3)² 9

n % 2 works correctly for negative numbers in Python

In Python, % always returns a non-negative result when the divisor is positive. So -3 % 2 == 1 (odd) and -4 % 2 == 0 (even) -- both behave as expected. This differs from some other languages where % can return negative values.

Solution approaches

def double_if_even_else_square(n):
    if n % 2 == 0:   # even check
        return 2 * n
    else:
        return n ** 2

def double_if_even_else_square(n):
    return 2 * n if n % 2 == 0 else n ** 2

double_if_even_else_square = lambda n: 2 * n if n % 2 == 0 else n ** 2

Key takeaways

01

Parity check: n % 2 == 0

The modulo operator % gives the remainder after division. n % 2 == 0 means no remainder when dividing by 2 -- the definition of even. Equivalently, n % 2 != 0 (or n % 2 == 1) means odd.

02

Ternary expression: a if condition else b

Python's inline conditional value_if_true if condition else value_if_false collapses a two-branch if/else into one line. Best used when both branches are short expressions, as here.

03

Exponentiation: n ** 2

** is Python's power operator. n ** 2 is equivalent to n * n but reads more naturally as "n squared". Both work; ** is preferred for clarity.