Smart contract concept in Blockchain / Solidity - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Solidity function call?

Consider this Solidity smart contract snippet:

pragma solidity ^0.8.0;

contract SimpleStorage {
    uint storedData;

    function set(uint x) public {
        storedData = x;
    }

    function get() public view returns (uint) {
        return storedData;
    }
}

If we call set(42) and then get(), what will get() return?

Blockchain / Solidity

pragma solidity ^0.8.0;

contract SimpleStorage {
    uint storedData;

    function set(uint x) public {
        storedData = x;
    }

    function get() public view returns (uint) {
        return storedData;
    }
}

A Transaction revert error

B 42

C Compilation error

D 0

💡 Hint

Think about what the set function does before calling get.

The set function stores the value 42 in storedData. Then get returns that stored value, so the output is 42.

🧠 Conceptual

intermediate

Which statement best describes a smart contract?

Choose the best description of a smart contract in blockchain technology.

A A centralized database storing user information securely.

B A legal contract signed digitally between two parties.

C A self-executing program that runs on a blockchain and enforces rules automatically.

D A cryptocurrency wallet used to store tokens.

💡 Hint

Think about what makes smart contracts different from traditional contracts.

Smart contracts are programs that run on blockchains and automatically enforce rules without intermediaries.

🔧 Debug

advanced

What error does this Solidity code produce?

Examine this Solidity function:

function divide(uint a, uint b) public pure returns (uint) {
    return a / b;
}

What happens if b is zero when calling divide(10, 0)?

Blockchain / Solidity

function divide(uint a, uint b) public pure returns (uint) {
    return a / b;
}

A Throws a division by zero runtime error and reverts the transaction

B Compiles with a warning but runs normally

C Returns 0

D Returns a large number due to overflow

💡 Hint

What happens in programming when you divide by zero?

Dividing by zero causes a runtime error in Solidity, which reverts the transaction.

📝 Syntax

advanced

Which option correctly declares a payable function in Solidity?

In Solidity, which function declaration allows the function to receive Ether?

A function deposit() public payable {}

B function deposit() public pay {}

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

D function deposit() public payable() {}

💡 Hint

Look for the correct keyword and syntax for payable functions.

The keyword payable must be used without parentheses to allow receiving Ether.

🚀 Application

expert

How many items are in the mapping after this transaction?

Given this Solidity contract snippet:

contract Registry {
    mapping(address => bool) public registered;

    function register() public {
        registered[msg.sender] = true;
    }
}

If three different users call register() once each, how many entries will registered contain?

A 1

B Cannot be determined

C 0

D 3

💡 Hint

Think about how mappings store data for unique keys.

Each unique address key set to true counts as one entry. Three users mean three entries.