First smart contract deployment in Blockchain / Solidity - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Solidity event emission?

Consider this simple smart contract that emits an event when deployed. What will be the value of the event's message when the contract is deployed?

Blockchain / Solidity

pragma solidity ^0.8.0;

contract HelloWorld {
    event Greet(string message);

    constructor() {
        emit Greet("Hello, Blockchain!");
    }
}

A "Hello, World!"

B No event emitted

C "Hello, Blockchain!"

D Compilation error

💡 Hint

Look at the string inside the emit Greet(...) statement in the constructor.

The constructor emits the Greet event with the message "Hello, Blockchain!" immediately upon deployment.

❓ Predict Output

intermediate

What is the value of the stored variable after deployment?

This contract stores a number passed during deployment. What will be the value of storedNumber after deployment with the argument 42?

Blockchain / Solidity

pragma solidity ^0.8.0;

contract StoreNumber {
    uint public storedNumber;

    constructor(uint _num) {
        storedNumber = _num;
    }
}

A 42

B 0

C Compilation error

D Undefined

💡 Hint

The constructor sets storedNumber to the input parameter _num.

The constructor assigns the input value 42 to the public variable storedNumber. So after deployment, storedNumber equals 42.

🔧 Debug

advanced

Why does this contract deployment fail?

Examine the contract below. When trying to deploy it, the deployment fails with a compilation error. What is the cause?

Blockchain / Solidity

pragma solidity ^0.8.0;

contract Counter {
    uint count;

    constructor() {
        count = 0;
    }
}

A Cannot assign zero to uint

B Missing semicolon after <code>count = 0</code>

C Constructor must have a visibility modifier

D State variable <code>count</code> must be public

💡 Hint

Check the syntax of the assignment line inside the constructor.

In Solidity, each statement must end with a semicolon. The line count = 0 is missing a semicolon, causing a compilation error.

🧠 Conceptual

advanced

Which statement about smart contract deployment is true?

Choose the correct statement about deploying a smart contract on Ethereum.

A Deployment stores the contract code and runs the constructor once

B Deployment runs the contract functions repeatedly until stopped

C Deployment requires no gas fees

D Deployment automatically grants admin rights to all users

💡 Hint

Think about what happens exactly once during deployment.

When a smart contract is deployed, its code is stored on the blockchain and the constructor function runs once to initialize state.

❓ Predict Output

expert

What is the output of this deployment and function call sequence?

Given this contract, what will be the output of calling getMessage() immediately after deployment?

Blockchain / Solidity

pragma solidity ^0.8.0;

contract Message {
    string private message;

    constructor() {
        setMessage("Welcome!");
    }

    function setMessage(string memory _msg) public {
        message = _msg;
    }

    function getMessage() public view returns (string memory) {
        return message;
    }
}

A Runtime error

B "" (empty string)

C Compilation error due to calling public function in constructor

D "Welcome!"

💡 Hint

The constructor calls setMessage with "Welcome!" before deployment finishes.

Calling a public function from the constructor is allowed. The message variable is set to "Welcome!" during deployment, so getMessage() returns "Welcome!".