REMIX:This contract does not implement all functions and thus cannot be created

Question

What should I do?

pragma solidity ^0.4.21;
contract ScoreInterface {
         function hit() public;
         function score() public view returns (uint);
}

This contract does not implement all functions and thus cannot be created

Answer 1

That's an Interface contract.

They are useful but they can't be deployed. They contain function signatures with no code blocks, so the EVM wouldn't know what to do - unacceptable.

An interface can provide a layer of protection for developer error.

contract Score is ScoreInterface {
  // now we are committed to implementing each function in ScoreInterface
  function hit() public {
    // do something
  }
  function score() public view returns (uint) {
    // do something
  }
}

Score will be deployable when each of those functions is defined.

Interfaces describe the surface area of a contract without describing the internal code. This is useful for other contracts that want to interact.

contract Game {

  function recordHit(address scoreContract) public {
    ScoreInterface s = ScoreInterface(scoreContract);
    s.hit();
  }
}

Hope it helps.

Answer 2

Read about Abstract Contracts you will get some more in depth understanding why this error is coming. https://solidity.readthedocs.io/en/v0.5.3/contracts.html#abstract-contract

Answer 3

You need to add some logic to your contract like this:

pragma solidity ^0.4.21;
contract ScoreInterface {
  function hit() public {
     // Some logic here
  }
  function score() public view returns (uint) {
     // Some logic here
  }
}

Actually, empty logic (as in my example) will work too, your contract will be able to deploy, but will do nothing when called.