Why Solidity is the language of Ethereum in Blockchain / Solidity - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a simple Solidity contract named MyContract.

Blockchain / Solidity

contract [1] {
    // contract code
}

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

AMyContract

BEthereum

CSolidity

DBlockchain

Attempts:

3 left

💡 Hint

Common Mistakes

Using reserved words like 'Solidity' or 'Ethereum' as contract names.

Using lowercase or invalid characters in the contract name.

The contract name must be a valid identifier. Here, MyContract is the correct name.

2fill in blank

medium

Complete the code to declare a public state variable of type uint named count.

Blockchain / Solidity

contract Counter {
    [1] public count;
}

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

Abool

Buint

Cstring

Daddress

Attempts:

3 left

💡 Hint

Common Mistakes

Using string for numeric values.

Using bool which only holds true or false.

The uint type is used for unsigned integers in Solidity, suitable for counting.

3fill in blank

hard

Fix the error in the function declaration to make it a public function that increments count.

Blockchain / Solidity

contract Counter {
    uint public count;
    function increment() [1] {
        count += 1;
    }
}

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

Aprivate

Bexternal

Cpublic

Dinternal

Attempts:

3 left

💡 Hint

Common Mistakes

Using private or internal which restrict access.

Omitting the visibility keyword entirely.

The function must be public to be called from outside the contract.

4fill in blank

hard

Fill both blanks to create a mapping from address to uint named balances and a function to update it.

Blockchain / Solidity

contract Wallet {
    mapping([1] => [2]) public balances;

    function updateBalance(address user, uint amount) public {
        balances[user] = amount;
    }
}

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

Aaddress

Buint

Cstring

Dbool

Attempts:

3 left

💡 Hint

Common Mistakes

Using string as key or value in mapping incorrectly.

Using bool which is not suitable for balances.

A mapping in Solidity links keys to values. Here, addresses map to unsigned integers.

5fill in blank

hard

Fill all three blanks to create a function that returns the balance of a given address.

Blockchain / Solidity

contract Wallet {
    mapping(address => uint) public balances;

    function getBalance([1] user) public view returns ([2]) {
        return balances[[3]];
    }
}

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

Aaddress

Buint

Cuser

Dbool

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong parameter types like bool.

Returning the wrong type or using incorrect variable names.

The function takes an address parameter named user and returns a uint balance.

Practice

1. Why is Solidity considered the main language for Ethereum smart contracts?

easy

A. Because it is a general-purpose programming language like Python

B. Because it is the oldest programming language available

C. Because it is used for building websites

D. Because it is specifically designed to work with Ethereum's blockchain

Solution

1. Step 1: Understand Solidity's purpose

   Solidity is created to write smart contracts that run on Ethereum's blockchain.

2. Step 2: Compare with other languages

   Unlike general-purpose languages, Solidity fits Ethereum's unique blockchain environment.

3. Final Answer:

   Because it is specifically designed to work with Ethereum's blockchain -> Option D

4. Quick Check:

   Solidity is Ethereum-specific = A [OK]

Hint: Solidity fits Ethereum blockchain needs specifically [OK]

Common Mistakes:

• Thinking Solidity is a general-purpose language
• Confusing Solidity with web development languages
• Assuming Solidity is the oldest language

2. Which of the following is the correct way to declare a state variable in Solidity?

easy

A. balance uint public;

B. int balance = 0

C. uint public balance;

D. var balance: uint;

Solution

1. Step 1: Recall Solidity variable syntax

   State variables are declared with type, visibility, and name, e.g., 'uint public balance;'.

2. Step 2: Check each option

   uint public balance; matches Solidity syntax; others have wrong order or missing semicolon.

3. Final Answer:

   uint public balance; -> Option C

4. Quick Check:

   Correct Solidity variable declaration = D [OK]

Hint: Remember: type visibility name; in Solidity [OK]

Common Mistakes:

• Omitting semicolon at the end
• Using wrong order of keywords
• Using 'var' which is not valid in Solidity

3. What will be the output of this Solidity function when called?

function getValue() public pure returns (uint) {
    uint a = 5;
    uint b = 10;
    return a + b;
}

medium

A. 15

B. 510

C. Error: missing return statement

D. 0

Solution

1. Step 1: Analyze the function logic

   The function adds two unsigned integers: 5 + 10.

2. Step 2: Calculate the sum

   5 + 10 equals 15, which is returned.

3. Final Answer:

   15 -> Option A

4. Quick Check:

   5 + 10 = 15 [OK]

Hint: Add numbers directly in return statement [OK]

Common Mistakes:

• Thinking numbers concatenate as strings
• Expecting a runtime error
• Missing return statement error

4. Identify the error in this Solidity code snippet:

contract Test {
    uint public count
    function increment() public {
        count += 1;
    }
}

medium

A. Missing semicolon after 'uint public count'

B. Function increment should be private

C. Variable count should be declared inside the function

D. No error, code is correct

Solution

1. Step 1: Check variable declaration syntax

   In Solidity, each statement must end with a semicolon; it's missing after 'uint public count'.

2. Step 2: Verify other parts

   Function visibility 'public' is correct; variable scope is appropriate.

3. Final Answer:

   Missing semicolon after 'uint public count' -> Option A

4. Quick Check:

   Semicolon missing = C [OK]

Hint: Every statement ends with a semicolon in Solidity [OK]

Common Mistakes:

• Ignoring missing semicolon errors
• Thinking function visibility must be private
• Declaring state variables inside functions

5. How does Solidity's design help automate agreements on Ethereum compared to traditional programming languages?

hard

A. It runs faster than all other programming languages

B. It includes built-in features for blockchain transactions and contract state management

C. It uses simple English-like syntax for all programming tasks

D. It requires no gas fees to execute contracts

Solution

1. Step 1: Understand Solidity's blockchain focus

   Solidity has special features to handle blockchain transactions and manage contract states automatically.

2. Step 2: Compare with other languages

   Traditional languages lack these blockchain-specific tools, making Solidity better for smart contracts.

3. Final Answer:

   It includes built-in features for blockchain transactions and contract state management -> Option B

4. Quick Check:

   Blockchain features in Solidity = B [OK]

Hint: Solidity has blockchain tools built-in [OK]

Common Mistakes:

• Assuming Solidity is the fastest language
• Believing Solidity uses English-like syntax for all tasks
• Thinking Solidity contracts execute without gas fees