Function declaration and syntax in Blockchain / Solidity - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple Solidity function

What is the output of this Solidity function when called with input 5?

Blockchain / Solidity

pragma solidity ^0.8.0;
contract Test {
    function multiplyByTwo(uint x) public pure returns (uint) {
        return x * 2;
    }
}

A 10

B 5

C 0

D Compilation error

💡 Hint

The function returns the input multiplied by 2.

The function multiplyByTwo takes an unsigned integer and returns its value multiplied by 2. So input 5 returns 10.

❓ Predict Output

intermediate

Return value of a function with multiple returns

What does this Solidity function return when called?

Blockchain / Solidity

pragma solidity ^0.8.0;
contract Test {
    function getValues() public pure returns (uint, bool) {
        return (42, true);
    }
}

A (42, true)

B 42

C true

D Compilation error

💡 Hint

The function returns two values as a tuple.

The function returns two values: an unsigned integer 42 and a boolean true as a tuple.

❓ Predict Output

advanced

Output of a function with state variable update

What is the value of the state variable after calling this function once?

Blockchain / Solidity

pragma solidity ^0.8.0;
contract Counter {
    uint public count = 0;
    function increment() public {
        count += 1;
    }
}

A Compilation error

B 0

C 1

D Undefined

💡 Hint

The function increases the count by 1.

The increment function adds 1 to the state variable count. Initially 0, after one call it becomes 1.

❓ Predict Output

advanced

Error type from incorrect function syntax

What error does this Solidity code produce?

Blockchain / Solidity

pragma solidity ^0.8.0;
contract Test {
    function wrongSyntax() public returns (uint) {
        return 5;
    }
}

A TypeError: Return type mismatch

B Runtime error

C No error, compiles fine

D SyntaxError: Missing semicolon

💡 Hint

Check the end of the return statement.

The return statement is missing a semicolon at the end, causing a syntax error.

🧠 Conceptual

expert

Function visibility and access control

Which function visibility keyword allows a function to be called only from within the contract or derived contracts?

A public

B internal

C external

D private

💡 Hint

Think about which keyword restricts access to the contract and its children.

The 'internal' keyword restricts function access to the contract itself and contracts that inherit from it.