Why Ethereum enables programmable money in Blockchain / Solidity - Challenge Your Understanding

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Solidity smart contract function?

Consider this simple Solidity function that returns the balance of an address in a token contract. What will be the output when calling getBalance() if the balance mapping has balances[msg.sender] = 100?

Blockchain / Solidity

pragma solidity ^0.8.0;

contract Token {
    mapping(address => uint) balances;

    constructor() {
        balances[msg.sender] = 100;
    }

    function getBalance() public view returns (uint) {
        return balances[msg.sender];
    }
}

A 0

B Revert error at runtime

C Compilation error

D 100

💡 Hint

Think about what the constructor does when the contract is deployed.

The constructor sets the balance of the deployer (msg.sender) to 100. Calling getBalance() from the deployer's address returns 100.

🧠 Conceptual

intermediate

Why does Ethereum enable programmable money?

Which of the following best explains why Ethereum allows money to be programmable?

A Ethereum uses a blockchain that supports smart contracts, which are self-executing code that can control digital assets automatically.

B Ethereum stores all money in a single centralized database controlled by one company.

C Ethereum only supports simple transactions without any code execution.

D Ethereum requires manual approval for every transaction by a central authority.

💡 Hint

Think about what smart contracts do on Ethereum.

Ethereum's blockchain supports smart contracts, which are programs that run automatically and can manage money based on rules coded into them.

🔧 Debug

advanced

Identify the error in this Solidity function for transferring tokens

This function is intended to transfer tokens from the sender to a recipient. What error will occur when this code runs?

Blockchain / Solidity

function transfer(address to, uint amount) public {
    require(balances[msg.sender] >= amount);
    balances[msg.sender] -= amount;
    balances[to] += amount;
}

A No error, the function works correctly.

B Revert error if balances[msg.sender] is less than amount.

C Compilation error due to missing return type.

D Runtime error if balances[to] overflows uint limit.

💡 Hint

Look at the require statement and what it checks.

The require statement causes the transaction to revert if the sender's balance is less than the amount, preventing the transfer.

📝 Syntax

advanced

Which option correctly declares a payable function in Solidity?

You want to write a function that can receive Ether. Which of these function declarations is syntactically correct?

A function deposit() payable public {}

B function deposit() public payble {}

C function deposit() public payable {}

D function deposit() public payable returns (uint) {}

💡 Hint

Check the spelling and order of keywords.

The correct syntax is function deposit() public payable {}. The keyword 'payable' must be spelled correctly and placed after visibility.

🚀 Application

expert

How does Ethereum ensure that smart contract code runs the same on all nodes?

Ethereum uses a special system to make sure every node runs smart contract code identically. Which mechanism achieves this?

A Ethereum uses the Ethereum Virtual Machine (EVM) which executes bytecode deterministically on all nodes.

B Ethereum relies on each node running different code versions to increase diversity.

C Ethereum nodes execute smart contracts using local machine instructions that vary by hardware.

D Ethereum uses a centralized server to run all smart contract code and broadcast results.

💡 Hint

Think about how Ethereum achieves consensus on contract execution.

The EVM is a virtual computer that runs the same bytecode on every node, ensuring consistent results and trustless execution.