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FizzBuzz

The classic programming interview question that tests loops and conditionals

FizzBuzz is perhaps the most famous programming interview question. It has become a standard test for basic programming competency because it requires understanding of loops, conditional statements, and the modulo operator.

📚 Concepts & Theory

FizzBuzz tests your understanding of several core programming concepts working together:

The Modulo Operator (%)

Returns the remainder after division:

10 % 3  # Returns 1 (10 ÷ 3 = 3 remainder 1)
15 % 5  # Returns 0 (15 ÷ 5 = 3 remainder 0)
15 % 3  # Returns 0 (15 ÷ 3 = 5 remainder 0)

If n % x == 0, then n is divisible by x.

The range() Function

Generates a sequence of numbers:

range(1, 21)     # 1 to 20 (end is exclusive)
range(5)         # 0 to 4
range(0, 10, 2)  # 0, 2, 4, 6, 8 (step of 2)

Condition Order Matters!

The key insight is checking for divisibility by BOTH 3 AND 5 first:

if n % 3 == 0 and n % 5 == 0:   # Check this FIRST
    print("FizzBuzz")
elif n % 3 == 0:
    print("Fizz")
elif n % 5 == 0:
    print("Buzz")
else:
    print(n)

If you check for 3 first, numbers like 15 would print "Fizz" instead of "FizzBuzz".

Alternative: Check 15 Directly

Since any number divisible by both 3 and 5 must be divisible by 15 (their LCM):

if n % 15 == 0:
    print("FizzBuzz")

🎯 Your Challenge

Write a program that prints numbers from 1 to 20. For multiples of 3, print "Fizz". For multiples of 5, print "Buzz". For multiples of both, print "FizzBuzz".

📝 Starter Code

Python

for i in range(1, 21):
    # Your logic here
    pass

Use the modulo operator (%) to check divisibility
Check for divisibility by BOTH 3 AND 5 first
Numbers divisible by both 3 and 5 are also divisible by 15
range(1, 21) gives you 1 through 20

Solution

Python

for i in range(1, 21):
    if i % 3 == 0 and i % 5 == 0:
        print("FizzBuzz")
    elif i % 3 == 0:
        print("Fizz")
    elif i % 5 == 0:
        print("Buzz")
    else:
        print(i)

Explanation

This solution iterates through 1-20, checking divisibility in the correct order: first both 3 AND 5, then just 3, then just 5. The key is checking the combined condition first.

⚠️ Common Mistakes to Avoid

Checking for 3 or 5 before checking for both
Using range(20) which starts at 0
Using = instead of == for comparison
Forgetting the colon after if/elif/else

❓ Frequently Asked Questions

FizzBuzz tests fundamental programming skills: loops, conditionals, modulo operator, and logical thinking. Despite its simplicity, many candidates struggle with it, making it an effective screening tool.

If you check for 3 first, a number like 15 would match and print Fizz before you ever check if it's also divisible by 5. By checking the combined condition first, you ensure FizzBuzz is printed for numbers like 15, 30, 45, etc.

The modulo operator (%) returns the remainder after division. For example, 15 % 3 returns 0 because 15 divides evenly by 3. If the result is 0, the number is divisible by the divisor.