Mappings in Blockchain / Solidity - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a mapping from address to uint.

Blockchain / Solidity

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

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

Aaccounts

Bbalance

Cbalances

Dusers

Attempts:

3 left

💡 Hint

Common Mistakes

Using singular names like 'balance' which is less common.

Using unrelated names like 'users' which is vague.

The mapping name is usually plural to represent multiple entries. balances is the common name for mapping addresses to uint values.

2fill in blank

medium

Complete the code to assign 100 to the sender's balance in the mapping.

Blockchain / Solidity

[1][msg.sender] = 100;

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

Abalances

Baddress

Cmapping

Dmsg

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'address' or 'msg' which are not mapping variables.

Trying to assign directly to 'mapping' keyword.

You assign a value to a key in the mapping by using the mapping name, here balances, with the key msg.sender.

3fill in blank

hard

Fix the error in the code to correctly check if an address has a balance greater than zero.

Blockchain / Solidity

if ([1][user] > 0) {
    // do something
}

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

Abalance

Baddress

Cmapping

Dbalances

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'balance' which is undefined.

Using 'mapping' or 'address' which are keywords or types, not variables.

The mapping variable name is balances. Using balances[user] accesses the stored value.

4fill in blank

hard

Fill both blanks to create a mapping from address to bool and set the sender's value to true.

Blockchain / Solidity

mapping([1] => [2]) public approved;
approved[msg.sender] = true;

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

Aaddress

Bbool

Cuint

Dstring

Attempts:

3 left

💡 Hint

Common Mistakes

Using uint or string as value type instead of bool.

Swapping key and value types.

The mapping key type is address and the value type is bool to store true/false values.

5fill in blank

hard

Fill all three blanks to create a mapping from uint to string, assign a value, and retrieve it.

Blockchain / Solidity

mapping([1] => [2]) public names;
names[[3]] = "Alice";
string memory name = names[1];

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

Auint

Bstring

C1

Daddress

Attempts:

3 left

💡 Hint

Common Mistakes

Using address as key type here instead of uint.

Using wrong key value like address or 0.

The mapping key is uint, the value is string, and the key used to assign is 1.