Nested while loops in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a nested while loop?

A nested while loop is a while loop inside another while loop. The inner loop runs completely for each iteration of the outer loop.

beginner

How does the flow of execution work in nested while loops?

The outer loop runs once, then the inner loop runs fully. After the inner loop finishes, the outer loop runs its next iteration, and the inner loop runs again, repeating this until the outer loop ends.

beginner

Write a simple example of nested while loops that prints a 3x3 grid of stars.

i = 1 while i <= 3: j = 1 while j <= 3: print('*', end=' ') j += 1 print() i += 1

intermediate

Why should you be careful with nested while loops?

Because if the inner or outer loop conditions never become false, the program can get stuck in an infinite loop, which means it keeps running forever.

beginner

How can nested while loops be useful in real life?

They help when you need to repeat tasks inside other repeated tasks, like printing tables, processing grids, or checking combinations of items.

What happens first in nested while loops?

A Both loops run at the same time

B The outer loop runs one iteration, then the inner loop runs fully

C The inner loop runs once, then the outer loop runs fully

D Only the outer loop runs

The outer loop starts and runs one iteration, then the inner loop runs completely before the outer loop continues.

What is a risk when using nested while loops?

A Infinite loops if conditions never become false

B The program runs too fast

C The loops skip iterations automatically

D The loops only run once

If the conditions controlling the loops never become false, the loops will run forever, causing an infinite loop.

How many times does the inner loop run if the outer loop runs 4 times and the inner loop runs 3 times each iteration?

A 3 times

B 4 times

C 12 times

D 7 times

The inner loop runs 3 times for each of the 4 outer loop iterations, so 4 x 3 = 12 times.

Which of these is a correct way to start a nested while loop?

A i = 0\nwhile i < 2:\n j = 0\n while j < 3:\n print(i, j)\n j += 1\n i += 1

B while i < 2:\n while j < 3:\n print(i, j)\n j += 1\n i += 1

C i = 0\nj = 0\nwhile i < 2 and j < 3:\n print(i, j)\n i += 1\n j += 1

D for i in range(2):\n while j < 3:\n print(i, j)\n j += 1

Option A correctly initializes counters and uses nested while loops with proper increments.

What will this code print? x = 1 while x <= 2: y = 1 while y <= 2: print(x, y) y += 1 x += 1

A 2 2 1 1 2 1 1 2

B 1 1 2 1 1 2 2 2

C 1 1 1 2 1 3 2 1

D 1 1 1 2 2 1 2 2

The outer loop runs for x=1 and x=2. For each x, the inner loop runs y=1 and y=2, printing pairs in order.

Explain how nested while loops work and give a simple example.

Think about loops inside loops and how they repeat.

Describe a real-life situation where nested while loops could be useful.

Imagine doing one task many times, and inside each, doing another task many times.