Contract structure and syntax in Blockchain / Solidity - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Solidity contract's function call?

Consider the following Solidity contract snippet. What will be the output when getValue() is called?

Blockchain / Solidity

pragma solidity ^0.8.0;

contract Simple {
    uint private value = 10;

    function getValue() public view returns (uint) {
        return value + 5;
    }
}

A Compilation error

B 10

C 15

D 5

💡 Hint

Look at the value of value and what getValue() returns.

The variable value is 10. The function returns value + 5, so the output is 15.

❓ Predict Output

intermediate

What error does this Solidity contract produce?

What error will occur when compiling this Solidity contract?

Blockchain / Solidity

pragma solidity ^0.8.0;

contract Test {
    uint public x;

    function setX(uint _x) public {
        x = _x;
    }

    function setX(uint _x) public {
        x = _x * 2;
    }
}

A Runtime error: Duplicate function call

B SyntaxError: Missing semicolon

C No error, compiles successfully

D TypeError: Function overloading not allowed with same parameter types

💡 Hint

Check if Solidity allows two functions with the same name and parameters.

Solidity does not allow two functions with the same name and parameter types. This causes a TypeError.

🔧 Debug

advanced

Why does this contract fail to compile?

Identify the reason this Solidity contract fails to compile.

Blockchain / Solidity

pragma solidity ^0.8.0;

contract Counter {
    uint count;

    function increment() public {
        count += 1;
    }

    function getCount() public view returns (uint) {
        return count;
    }
}

A Variable <code>count</code> is not initialized

B Missing semicolon after <code>count += 1</code>

C Function <code>increment</code> must be declared <code>view</code>

D Return type of <code>getCount</code> is incorrect

💡 Hint

Look carefully at the line inside increment().

The line count += 1 is missing a semicolon at the end, causing a syntax error.

🧠 Conceptual

advanced

What is the visibility of the variable data in this contract?

Given this Solidity contract, what is the visibility of the variable data?

Blockchain / Solidity

pragma solidity ^0.8.0;

contract Storage {
    string data;

    function setData(string memory _data) public {
        data = _data;
    }

    function getData() public view returns (string memory) {
        return data;
    }
}

A Internal (accessible in this contract and derived contracts)

B Public (accessible from outside the contract)

C External (only callable from outside)

D Private (only accessible inside the contract)

💡 Hint

State variables without explicit visibility are internal by default in Solidity.

In Solidity, state variables without a visibility modifier are internal by default, so data is internal.

❓ Predict Output

expert

What is the output of this contract's function call with inheritance?

Consider these two contracts. What will be the output of getName() when called on Child?

Blockchain / Solidity

pragma solidity ^0.8.0;

contract Parent {
    function getName() public pure virtual returns (string memory) {
        return "Parent";
    }
}

contract Child is Parent {
    function getName() public pure override returns (string memory) {
        return "Child";
    }
}

A "Child"

B "Parent"

C Compilation error due to missing override keyword

D Runtime error: Function not found

💡 Hint

Look at how getName() is overridden in Child.

The Child contract overrides getName() and returns "Child".