Nested loops in C++ - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a nested loop in C++?

A nested loop is a loop inside another loop. The inner loop runs completely every time the outer loop runs once.

beginner

How many times will the inner loop run in this code?<br>

for(int i = 0; i < 3; i++) {<br>  for(int j = 0; j < 2; j++) {<br>    // inner loop body<br>  }<br>}

The inner loop runs 2 times for each of the 3 outer loop runs, so 3 × 2 = 6 times in total.

beginner

Why do we use nested loops?

We use nested loops to work with multi-dimensional data, like tables or grids, or to repeat tasks inside other repeated tasks.

intermediate

What happens if the inner loop depends on the outer loop variable?

The inner loop can change how many times it runs based on the outer loop variable, allowing more flexible patterns.

beginner

Write a nested loop to print a 3x3 grid of stars (*) in C++.

for(int i = 0; i < 3; i++) {<br>  for(int j = 0; j < 3; j++) {<br>    std::cout << "* ";<br>  }<br>  std::cout << std::endl;<br>}

How many times does the inner loop run in this code?<br>

for(int i = 0; i < 4; i++) {<br>  for(int j = 0; j < 3; j++) {<br>    // code<br>  }<br>}

A 12

B 7

C 4

D 3

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

What is the output of this nested loop?<br>

for(int i = 1; i <= 2; i++) {<br>  for(int j = 1; j <= 2; j++) {<br>    std::cout << i+j << " ";<br>  }<br>  std::cout << std::endl;<br>}

A 1 1 \n 2 2

B 1 2 \n 2 3

C 2 3 \n 3 4

D 3 4 \n 4 5

For i=1: j=1 (1+1=2), j=2 (1+2=3); for i=2: j=1 (2+1=3), j=2 (2+2=4).

Which statement is true about nested loops?

A Inner loop runs completely for each outer loop iteration.

B Outer loop runs completely for each inner loop iteration.

C Both loops run only once.

D Nested loops cannot be used with for loops.

The inner loop finishes all its iterations every time the outer loop runs once.

What is the time complexity of two nested loops each running n times?

A O(n)

B O(n^2)

C O(1)

D O(log n)

Two nested loops each running n times result in n × n = n² operations.

How can nested loops be useful in real life?

A To avoid repeating tasks.

B To print a single number once.

C To run only one loop.

D To process rows and columns in a table.

Nested loops help handle multi-dimensional data like tables or grids.

Explain what nested loops are and give a simple example in C++.

Think about loops inside loops and how many times the inner loop runs.

Describe a real-world scenario where nested loops would be useful.

Imagine rows and columns or a chessboard.