Using for directive in Blockchain / Solidity - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple for directive loop

What is the output of this blockchain smart contract snippet using a for directive to iterate over transactions?

Blockchain / Solidity

let total = 0;
for (let i = 0; i < 3; i++) {
  total += i * 10;
}
console.log(total);

A 30

B 60

C 0

D SyntaxError

💡 Hint

Remember the loop runs from 0 to 2, adding i*10 each time.

The loop runs with i = 0, 1, 2. The sums are 0*10 + 1*10 + 2*10 = 0 + 10 + 20 = 30.

🧠 Conceptual

intermediate

Understanding for directive in blockchain event processing

In a blockchain smart contract, which best describes the purpose of a for directive when processing a list of events?

A To repeat actions for each event in the list sequentially

B To execute only the first event and skip the rest

C To randomly select events to process

D To permanently stop the contract execution

💡 Hint

Think about how loops help handle multiple items.

A for directive repeats code for each item in a list, allowing sequential processing of all events.

🔧 Debug

advanced

Identify the error in this for directive code

What error does this blockchain smart contract code produce?

Blockchain / Solidity

for (let i = 0; i < 5; i++) {
  console.log(i);
}

A ReferenceError because console is undefined

B TypeError because i is not defined

C SyntaxError due to missing parentheses in for loop

D No error, prints numbers 0 to 4

💡 Hint

Check the syntax of the for loop header.

The for loop syntax requires parentheses around the initialization, condition, and increment parts.

❓ Predict Output

advanced

Output of nested for directives in blockchain code

What is the output of this nested for directive code snippet?

Blockchain / Solidity

let result = '';
for (let i = 1; i <= 2; i++) {
  for (let j = 1; j <= 2; j++) {
    result += `${i}${j} `;
  }
}
console.log(result.trim());

A "1 2 1 2"

B "12 11 22 21"

C "SyntaxError"

D "11 12 21 22"

💡 Hint

The outer loop controls the first digit, inner loop the second.

The outer loop runs i=1,2; inner loop runs j=1,2; concatenating pairs in order: 11 12 21 22.

🚀 Application

expert

Calculating total token transfers using for directive

Given this blockchain code snippet that sums token transfers, what is the final value of totalTokens?

Blockchain / Solidity

const transfers = [100, 200, 50, 150];
let totalTokens = 0;
for (const amount of transfers) {
  if (amount > 100) {
    totalTokens += amount;
  }
}
console.log(totalTokens);

A 500

B 350

C 100

D SyntaxError

💡 Hint

Add only amounts greater than 100.

Only 200 and 150 are greater than 100, so totalTokens = 200 + 150 = 350.