For and while loops in Blockchain / Solidity - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a for loop used for?

A for loop repeats a block of code a set number of times, like counting steps in a recipe.

beginner

What does a while loop do?

A while loop keeps running code as long as a condition is true, like waiting for a traffic light to turn green.

intermediate

How do you stop a while loop from running forever?

You make sure the condition will become false at some point, like counting down to zero.

intermediate

Give an example of a for loop in blockchain smart contract code.

In Solidity, a for loop can count through an array of addresses to check balances or permissions.

advanced

Why should loops be used carefully in blockchain smart contracts?

Because loops can use a lot of gas (cost) if they run many times, making the contract expensive to use.

What is the main difference between a for loop and a while loop?

A For loops run forever; while loops run once.

B For loops run a set number of times; while loops run until a condition is false.

C While loops run a set number of times; for loops run until a condition is false.

D There is no difference.

For loops repeat a fixed number of times, while loops continue as long as a condition is true.

In blockchain smart contracts, why is it risky to use loops that run many times?

A They make the contract run faster.

B They reduce the contract's security.

C They can cause the contract to run out of gas and fail.

D They automatically stop after 10 iterations.

Loops that run many times use more gas, which can cause the contract to run out of gas and fail.

Which loop is best when you know exactly how many times to repeat an action?

A For loop

B If statement

C While loop

D Switch statement

For loops are ideal when the number of repetitions is known beforehand.

What happens if a while loop's condition never becomes false?

A The loop runs forever (infinite loop).

B The loop runs once.

C The program crashes immediately.

D The loop stops automatically.

If the condition never becomes false, the while loop runs forever, causing an infinite loop.

In Solidity, which keyword is used to start a for loop?

A repeat

B loop

C while

D for

The keyword 'for' is used to start a for loop in Solidity.

Explain how a for loop works and give a simple example in blockchain code.

Think about repeating actions a fixed number of times.

Describe why while loops can be risky in blockchain smart contracts and how to avoid problems.

Consider what happens if the loop never stops.