View and pure functions in Blockchain / Solidity - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a view function call

Consider this Solidity contract snippet with a view function. What will be the output when calling getBalance() after deployment?

Blockchain / Solidity

contract Wallet {
    uint private balance = 100;
    
    function getBalance() public view returns (uint) {
        return balance;
    }
}

A Transaction rejected

B 0

C Compilation error

D 100

💡 Hint

View functions read state without changing it.

The getBalance() function is a view function that returns the stored balance which is initialized to 100. Calling it does not change state and returns 100.

❓ Predict Output

intermediate

Pure function output with parameters

What is the output of calling add(5, 3) in this Solidity contract?

Blockchain / Solidity

contract Calculator {
    function add(uint a, uint b) public pure returns (uint) {
        return a + b;
    }
}

A Compilation error

B 8

C 0

D Transaction reverted

💡 Hint

Pure functions return values based only on inputs.

The add function is pure and returns the sum of a and b. Calling add(5, 3) returns 8.

❓ Predict Output

advanced

Effect of modifying state in a view function

What happens when this contract is compiled and deployed?

Blockchain / Solidity

contract Test {
    uint x = 10;
    
    function wrongView() public view returns (uint) {
        x = 20;
        return x;
    }
}

A Returns 10

B Returns 20

C Compilation error due to state modification in view function

D Runtime error when calling wrongView

💡 Hint

View functions cannot modify state variables.

The wrongView function tries to modify the state variable x inside a view function, which is not allowed and causes a compilation error.

❓ Predict Output

advanced

Pure function calling a view function

What error occurs when compiling this contract?

Blockchain / Solidity

contract Mixed {
    uint y = 5;
    
    function getY() public view returns (uint) {
        return y;
    }
    
    function pureCaller() public pure returns (uint) {
        return getY();
    }
}

A Compilation error: pure function cannot call view function

B Runtime error when calling pureCaller

C Returns 0

D Returns 5

💡 Hint

Pure functions cannot read or modify state or call view functions.

The pureCaller function is declared pure but calls getY, a view function that reads state. This is disallowed and causes a compilation error.

🧠 Conceptual

expert

Gas cost difference between view and pure functions

Which statement about gas costs when calling view and pure functions externally (via call) is correct?

A Both view and pure functions called externally cost no gas

B View functions cost gas, pure functions do not

C Both view and pure functions always cost gas

D Pure functions cost gas, view functions do not

💡 Hint

External calls to view or pure functions do not change blockchain state.

When called externally (not in a transaction), both view and pure functions do not consume gas because they do not modify state and run locally on the node.