Description
Both CharityRegistry.sol and GivingThanks.sol are using floating versions of solidity.
When using floating version of solidity the code can be run by compiler of older version that can have some functionalities not working.

Impact
In older versions of Solidity, certain features are unavailable, and it's recommended to use the latest version for enhanced security and functionality.

Recommended mitigation
To mitigate these issues, specify an exact version of Solidity instead of a floating version. This ensures that the contract benefits from the latest security improvements and language features within that version.