Efficient data structures in Blockchain / Solidity - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a mapping in Solidity that links addresses to balances.

Blockchain / Solidity

mapping(address => uint) public [1];

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

Ausers

Bbalance

Caccounts

Dbalances

Attempts:

3 left

💡 Hint

Common Mistakes

Using singular form like 'balance' which is less common for mappings.

Using unrelated names like 'users' which do not describe balances.

The mapping name balances is commonly used to store user balances in Solidity smart contracts.

2fill in blank

medium

Complete the code to add a new element to a dynamic array in Solidity.

Blockchain / Solidity

uint[] public numbers;

function addNumber(uint num) public {
    numbers.[1](num);
}

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Aappend

Binsert

Cpush

Dadd

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'append' which is a Python method, not Solidity.

Using 'insert' which requires an index in Solidity.

The push function adds a new element to the end of a dynamic array in Solidity.

3fill in blank

hard

Fix the error in the code to correctly check if a key exists in a mapping.

Blockchain / Solidity

mapping(address => uint) public balances;

function hasBalance(address user) public view returns (bool) {
    return balances[[1]] != 0;
}

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Amsg.sender

Buser

Caddress

Dthis

Attempts:

3 left

💡 Hint

Common Mistakes

Using msg.sender which checks the caller, not the input address.

Using address which is a type, not a variable.

The function parameter user should be used to check the balance in the mapping.

4fill in blank

hard

Fill both blanks to create a struct and declare a mapping from address to that struct.

Blockchain / Solidity

struct [1] {
    uint balance;
    uint lastUpdated;
}

mapping(address => [2]) public accounts;

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

AAccount

BUser

DBalance

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names for the struct and mapping type.

Using unrelated names like 'Balance' which is a field, not a struct.

The struct is named Account and the mapping uses the same struct type.

5fill in blank

hard

Fill all three blanks to create a mapping with a nested mapping for token balances.

Blockchain / Solidity

mapping(address => mapping([1] => uint)) public [2];

function getBalance(address user, [3] token) public view returns (uint) {
    return [2][user][token];
}

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

Aaddress

Bbalances

Dtokens

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect key types like 'uint' for tokens.

Using inconsistent names for the mapping and function parameters.

The nested mapping uses address as the key type for tokens, the mapping is named balances, and the function parameter for token is an address.