Storage vs memory usage in Blockchain / Solidity - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a storage variable in Solidity.

Blockchain / Solidity

uint256 public [1];

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

AstoredValue

BmemoryValue

CtempValue

DlocalValue

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing a variable name that implies temporary or memory usage.

Confusing storage with memory keyword.

In Solidity, variables declared at contract level like storedValue are stored in storage by default.

2fill in blank

medium

Complete the function to declare a memory array parameter in Solidity.

Blockchain / Solidity

function processData(uint256[] [1] data) public {}

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

Apersistent

Bmemory

Ccalldata

Dstorage

Attempts:

3 left

💡 Hint

Common Mistakes

Using storage for function parameters which causes errors.

Confusing calldata with memory.

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

3fill in blank

hard

Fix the error in the function by choosing the correct data location for the string parameter.

Blockchain / Solidity

function setName(string [1] name) public {}

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

Astorage

Bpersistent

Cmemory

Dcalldata

Attempts:

3 left

💡 Hint

Common Mistakes

Using memory unnecessarily which increases gas cost.

Using storage which is invalid for function parameters.

For external function parameters, calldata is the recommended data location for strings to save gas and avoid copying.

4fill in blank

hard

Fill the blank to create a temporary memory array for the function return. Mappings are always stored in storage.

Blockchain / Solidity

mapping(address => uint) balances;
function getTopBalances() public view returns (uint[] {{BLANK_2}}) {}

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

Astorage

Bcalldata

Cmemory

Dpersistent

Attempts:

3 left

💡 Hint

Common Mistakes

Declaring mapping as memory which is invalid.

Returning arrays without specifying memory location.

Mappings are always stored in storage (no keyword needed). Function return arrays should be declared as memory to hold temporary data.

5fill in blank

hard

Fill both blanks to declare a memory struct variable and assign a value.

Blockchain / Solidity

struct User {
    uint id;
    string name;
}
User [2] userMemory;
userMemory.id = {{BLANK_3}};

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

Astorage

Bmemory

C10

Dcalldata

Attempts:

3 left

💡 Hint

Common Mistakes

Declaring struct with memory keyword which is invalid.

Assigning a string instead of a number to id.

The struct is declared at the contract level. The variable userMemory is declared in memory for temporary use. Assigning 10 to id sets the value.