Virtual and override keywords in Blockchain / Solidity - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a virtual function in a smart contract.

Blockchain / Solidity

contract Base {
    function greet() public view [1] returns (string memory) {
        return "Hello from Base";
    }
}

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

Aexternal

Bvirtual

Coverride

Dpure

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'override' instead of 'virtual' when declaring the base function.

Omitting the keyword entirely, which prevents overriding.

The virtual keyword marks a function that can be overridden in a derived contract.

2fill in blank

medium

Complete the code to override the virtual function in the derived contract.

Blockchain / Solidity

contract Derived is Base {
    function greet() public view [1] returns (string memory) {
        return "Hello from Derived";
    }
}

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

Aoverride

Bpure

Cexternal

Dvirtual

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'virtual' instead of 'override' when overriding a function.

Forgetting to mark the base function as virtual.

The override keyword is used to replace the behavior of a virtual function in a child contract.

3fill in blank

hard

Fix the error in the derived contract by adding the correct keyword to the overridden function.

Blockchain / Solidity

contract Derived is Base {
    function greet() public view [1] returns (string memory) {
        return "Hello from Derived";
    }
}

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

Aoverride

Bvirtual

Cexternal

Dpayable

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'virtual' instead of 'override' in the derived contract.

Omitting the keyword entirely, causing a compilation error.

The overridden function must use the override keyword to compile correctly.

4fill in blank

hard

Fill both blanks to declare a virtual function and override it correctly.

Blockchain / Solidity

contract Base {
    function calculate() public view [1] returns (uint) {
        return 1;
    }
}

contract Derived is Base {
    function calculate() public view [2] returns (uint) {
        return 2;
    }
}

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

Avirtual

Bexternal

Coverride

Dpure

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'override' in the base function instead of 'virtual'.

Forgetting to use 'override' in the derived function.

The base function uses virtual to allow overriding, and the derived function uses override to replace it.

5fill in blank

hard

Fill all three blanks to declare a virtual function, override it, and call the base function inside the override.

Blockchain / Solidity

contract Base {
    function info() public view [3] returns (string memory) {
        return "Base info";
    }
}

contract Derived is Base {
    function info() public view [1] returns (string memory) {
        return string(abi.encodePacked(Base.[2](), " and Derived info"));
    }
}

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

Aoverride

Binfo

Cvirtual

Dpure

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'virtual' instead of 'override' in the derived function.

Calling a wrong function name instead of the base function.

Not marking the base function as virtual.

The derived function uses override to replace the base function, calls the base function by its name info, and the base function is marked virtual.