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

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a function parameter stored in memory.

Blockchain / Solidity

function greet(string [1] name) public pure returns (string memory) {
    return name;
}

Drag options to blanks, or click blank then click option'

Astorage

Bcalldata

Cvar

Dmemory

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'storage' for function parameters causes errors.

Using 'var' is not valid in Solidity.

Function parameters that are strings or arrays usually use memory to store temporary data during function execution.

2fill in blank

medium

Complete the code to declare a function parameter that is read-only and cheaper to use.

Blockchain / Solidity

function readData(string [1] data) external view returns (string memory) {
    return data;
}

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Astorage

Bcalldata

Cmemory

Dconstant

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'memory' instead of 'calldata' increases gas cost.

Trying to modify calldata variables causes errors.

calldata is used for function parameters that are read-only and passed from external calls, saving gas.

3fill in blank

hard

Fix the error in the code by choosing the correct data location for the state variable.

Blockchain / Solidity

contract Example {
    string [1] name;

    function setName(string memory newName) public {
        name = newName;
    }
}

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Acalldata

Bmemory

Cstorage

Dconstant

Attempts:

3 left

💡 Hint

Common Mistakes

Declaring state variables as 'memory' causes compilation errors.

Using 'calldata' for state variables is invalid.

State variables must be stored in storage because they persist on the blockchain.

4fill in blank

hard

Complete the code to create a function that accepts a read-only array and stores it in state.

Blockchain / Solidity

contract DataStore {
    uint[] public data;

    function storeData(uint[] [1] input) public {
        data = input;
    }
}

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Acalldata

Bmemory

C.slice()

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to call .slice() on calldata arrays causes errors.

Using memory instead of calldata increases gas cost.

The function parameter uses calldata for a read-only array. The assignment copies the array directly, so no extra method is needed.

5fill in blank

hard

Fill both blanks to declare a function that modifies a storage array using a memory copy.

Blockchain / Solidity

contract Modify {
    uint[] public numbers;

    function updateNumbers(uint[] [1] newNumbers) public {
        uint[] storage nums = numbers;
        nums = newNumbers;
        nums.push([2]);
    }
}

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Amemory

C100

Dcalldata

Attempts:

3 left

💡 Hint

Common Mistakes

Using calldata prevents modification.

Trying to assign calldata array directly to storage without copying.

The function parameter uses memory to hold the new array. The assignment copies the array. Then, 100 is pushed to the storage array.