Data types (uint, int, bool, address, string) in Blockchain / Solidity - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Solidity code snippet?

Consider the following Solidity function that returns a boolean and an integer:

function test() public pure returns (bool, int) {
    int a = -10;
    bool b = a < 0;
    return (b, a * 2);
}

What will be the returned values?

Blockchain / Solidity

function test() public pure returns (bool, int) {
    int a = -10;
    bool b = a < 0;
    return (b, a * 2);
}

A (false, -20)

B (false, 20)

C (true, 20)

D (true, -20)

💡 Hint

Remember that int can hold negative values and the comparison a < 0 checks if a is negative.

The variable a is -10, which is less than 0, so b is true. Multiplying -10 by 2 gives -20.

❓ Predict Output

intermediate

What is the value of the address variable after assignment?

Given this Solidity code snippet:

address addr = 0x1234567890123456789012345678901234567890;
address zeroAddr = address(0);
bool isZero = (addr == zeroAddr);

What is the value of isZero?

Blockchain / Solidity

address addr = 0x1234567890123456789012345678901234567890;
address zeroAddr = address(0);
bool isZero = (addr == zeroAddr);

A true

B Compilation error

C false

D Runtime error

💡 Hint

The zero address is a special address with all zeros. Check if addr matches it.

The addr is a non-zero address, so comparing it to address(0) results in false.

❓ Predict Output

advanced

What is the output of this Solidity string comparison?

Consider this Solidity function:

function compareStrings() public pure returns (bool) {
    string memory a = "hello";
    string memory b = "hello";
    return keccak256(bytes(a)) == keccak256(bytes(b));
}

What does this function return?

Blockchain / Solidity

function compareStrings() public pure returns (bool) {
    string memory a = "hello";
    string memory b = "hello";
    return keccak256(bytes(a)) == keccak256(bytes(b));
}

A false

B true

C Compilation error

D Runtime error

💡 Hint

Strings in Solidity cannot be compared directly. Instead, their hashes are compared.

Both strings are "hello", so their keccak256 hashes are equal, returning true.

❓ Predict Output

advanced

What error does this Solidity code raise?

Analyze this Solidity snippet:

uint8 x = 255;
x = x + 1;

What happens when this code runs?

Blockchain / Solidity

uint8 x = 255;
x = x + 1;

A Overflow error (runtime revert in Solidity 0.8+)

B x becomes 0 without error

C Compilation error

D x becomes 256

💡 Hint

Since Solidity 0.8, arithmetic overflow causes a runtime error.

Adding 1 to 255 (max for uint8) causes overflow, triggering a runtime revert error.

🧠 Conceptual

expert

Which data type is best suited for storing Ethereum wallet addresses?

In Solidity, which data type should you use to store Ethereum wallet addresses securely and efficiently?

A address

B uint256

C string

D bool

💡 Hint

Ethereum addresses have a special data type designed for them.

The address type is specifically designed to store Ethereum wallet addresses, providing built-in safety and utility functions.