Iteration & Accumulation — Lesson 3: Count matches in a range

New skill: Counters, modulo, and conditional loops
Previously learned: Unit 05 — conditional execution

Why this matters

You can combine an if statement with a loop to count how many numbers meet a rule.

Study this example

count = 0
for n in range(1, 7):
    if n % 2 == 0:
        count += 1
print(count)

The modulo operator % gives the remainder. Values divisible by 2 have a remainder of 0; among 1 through 6, there are three even numbers.

Before moving on, predict the result of the program or function. Then run it and compare.

Check your understanding

How many even numbers are there from 1 through 9?

Common mistake

Increment the count only if a number satisfies the condition, not on every loop iteration.

Practice

Complete count_multiples_of_three(limit) to return how many positive integers from 1 through limit, inclusive are divisible by 3. limit is a nonnegative integer.

Public example 1

Input

count_multiples_of_three(10)

Output

3

Public example 2

Input

count_multiples_of_three(3)

Output

1

Public example 3

Input

count_multiples_of_three(2)

Output

0

Public example 4

Input

count_multiples_of_three(15)

Output

5

Open the Python starter

Hint 1

Which operator checks if division has no remainder?

Hint 2

Visit each integer in the inclusive interval.

Hint 3

Only increase the counter for numbers divisible by 3.

Reflection

Explain why your solution works and describe one boundary case you tried.