Blockchain use cases beyond crypto - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this smart contract function?

Consider a smart contract function that stores and retrieves a document hash for supply chain tracking. What will be the output after calling getDocumentHash()?

Blockchain / Solidity

contract SupplyChain {
    string private documentHash;

    function storeDocumentHash(string memory hash) public {
        documentHash = hash;
    }

    function getDocumentHash() public view returns (string memory) {
        return documentHash;
    }
}

// After calling storeDocumentHash("abc123hash")
// What does getDocumentHash() return?

A "abc123hash"

B "documentHash"

C ""

D null

💡 Hint

Think about what value is stored and returned by the function.

The function storeDocumentHash saves the string "abc123hash" in the private variable documentHash. The getDocumentHash function returns this stored value, so the output is "abc123hash".

🧠 Conceptual

intermediate

Which blockchain feature best supports secure medical record sharing?

In healthcare, sharing patient records securely is critical. Which blockchain feature helps ensure data integrity and controlled access?

A Proof of Work mining

B Anonymous public transactions

C Immutable ledger with permissioned access

D Unlimited data storage on-chain

💡 Hint

Consider how data can be protected and shared only with authorized parties.

An immutable ledger ensures records cannot be changed once stored, and permissioned access restricts who can view or add data, making it ideal for sensitive medical records.

🔧 Debug

advanced

Why does this blockchain voting contract fail to count votes correctly?

Review the following simplified voting contract code. Why does the vote count remain zero after voting?

Blockchain / Solidity

contract Voting {
    mapping(address => bool) public voters;
    uint public voteCount;

    function vote() public {
        if (!voters[msg.sender]) {
            voters[msg.sender] = true;
            voteCount = voteCount + 1;
        }
    }

    function getVotes() public view returns (uint) {
        return voteCount;
    }
}

// After calling vote() from different addresses, voteCount is still 0.

A The contract is deployed but vote() is never called successfully due to missing payable modifier

B The voteCount variable is private and cannot be read

C The mapping voters is not initialized, causing voteCount to reset

D The voteCount variable is not updated because vote() is never executed in a transaction

💡 Hint

Think about how blockchain state changes happen and what is needed to update state variables.

State changes like incrementing voteCount require a transaction that modifies the blockchain state. If vote() is called as a view or call (not a transaction), voteCount won't update.

📝 Syntax

advanced

Which option fixes the syntax error in this blockchain identity contract snippet?

Identify the correct fix for the syntax error in this Solidity code snippet:

mapping(address => string) public identities

function setIdentity(string memory name) public {
    identities[msg.sender] = name;
}

A Add a semicolon after the mapping declaration

B Add <code>public</code> keyword to the function setIdentity

C Change <code>string</code> to <code>string memory</code> in mapping

D Replace <code>msg.sender</code> with <code>address(this)</code>

💡 Hint

Check the end of the mapping declaration line.

In Solidity, each statement must end with a semicolon. The mapping declaration is missing a semicolon.

🚀 Application

expert

How many unique assets are tracked after these blockchain transactions?

A blockchain asset tracking contract stores assets by unique IDs. After these transactions, how many unique assets are stored?

storeAsset(101, "Car")
storeAsset(102, "Bike")
storeAsset(101, "Truck")
storeAsset(103, "Boat")
storeAsset(102, "Scooter")

A 2

B 3

C 5

D 4

💡 Hint

Consider that storing an asset with an existing ID overwrites the previous one.

Asset IDs 101, 102, and 103 are used. The second storeAsset calls with IDs 101 and 102 overwrite previous entries. So, there are 3 unique assets stored.