Storage vs memory vs calldata in Blockchain / Solidity - Practice Questions

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Solidity function?

Consider the following Solidity function that modifies an array passed as memory and storage. What will be the final value of myArray after calling modifyArrays?

Blockchain / Solidity

pragma solidity ^0.8.0;

contract Test {
    uint[] public myArray = [1, 2, 3];

    function modifyArrays(uint[] memory memArray) public {
        memArray[0] = 100;
        myArray[1] = 200;
    }
}

A [100, 200, 3]

B [1, 2, 3]

C [100, 2, 3]

D [1, 200, 3]

💡 Hint

Remember that memory arrays are copies and changes to them do not affect storage arrays.

The memArray is a copy of the array passed in memory. Changing memArray[0] does not affect myArray. However, myArray[1] is changed directly in storage, so it updates to 200.

❓ Predict Output

intermediate

What error occurs when modifying calldata array?

What happens if you try to modify a calldata array inside a Solidity function?

Blockchain / Solidity

pragma solidity ^0.8.0;

contract Test {
    function modifyCalldata(uint[] calldata data) public pure {
        data[0] = 10;
    }
}

A Function executes successfully, data[0] changed

B Compilation error: Cannot assign to calldata array element

C Runtime error: Out of gas

D Warning: Unused variable data

💡 Hint

Think about the mutability of calldata parameters.

calldata is read-only. Trying to assign a value to an element causes a compilation error.

🧠 Conceptual

advanced

Why use calldata over memory for function parameters?

Which of the following is the main advantage of using calldata instead of memory for external function parameters in Solidity?

A Calldata is cheaper in gas because it avoids copying data

B Calldata variables can be resized dynamically

C Calldata variables persist after function execution

D Calldata allows modifying the input parameters

💡 Hint

Think about how data is passed and stored in Ethereum transactions.

calldata is a read-only area where function arguments are stored. Using it avoids copying data into memory, saving gas.

❓ Predict Output

advanced

What is the output of this storage vs memory example?

What will be the output of the following Solidity code snippet?

Blockchain / Solidity

pragma solidity ^0.8.0;

contract Test {
    uint[] public arr = [1, 2, 3];

    function test() public returns (uint) {
        uint[] storage ref = arr;
        uint[] memory copy = arr;
        ref[0] = 10;
        copy[1] = 20;
        return arr[0] + arr[1];
    }
}

A 12

B 3

C 21

D Compilation error

💡 Hint

Remember that storage references affect the original array, but memory copies do not.

Changing ref[0] changes arr[0] to 10. Changing copy[1] does not affect arr. So sum is 10 + 2 = 12.

🧠 Conceptual

expert

How does storage layout affect gas cost in Solidity?

Which statement best explains how storage layout impacts gas costs in Solidity smart contracts?

A Storage layout does not affect gas costs as all variables cost the same

B Storage variables are cheaper to access than memory variables

C Accessing and modifying <code>storage</code> variables is expensive because it involves writing to the blockchain state

D Using <code>calldata</code> increases gas cost compared to storage

💡 Hint

Think about what happens when you change data stored on the blockchain.

Writing to storage costs more gas because it changes the blockchain state, which requires consensus and persistence.