code questions on remix, "_currentIndex" and "_ownerships"

[yzh617]

Hi

I paste the YourNftToken.sol on the remix, and there is an error code on compile.
the variable "_currentIndex" and "_ownerships", I did not find any declaration for the variable,
some one know why? thanks for the big help.

function walletOfOwner(address _owner) public view returns (uint256[] memory) {
uint256 ownerTokenCount = balanceOf(_owner);
uint256[] memory ownedTokenIds = new uint256[](ownerTokenCount);
uint256 currentTokenId = _startTokenId();
uint256 ownedTokenIndex = 0;
address latestOwnerAddress;

while (ownedTokenIndex < ownerTokenCount && currentTokenId < _currentIndex) {
  TokenOwnership memory ownership = _ownerships[currentTokenId];

  if (!ownership.burned) {
    if (ownership.addr != address(0)) {
      latestOwnerAddress = ownership.addr;
    }

    if (latestOwnerAddress == _owner) {
      ownedTokenIds[ownedTokenIndex] = currentTokenId;

      ownedTokenIndex++;
    }
  }

  currentTokenId++;
}

return ownedTokenIds;

}

[sal-420]

I did the same. what fixed was changing the progma line to: pragma solidity >=0.8.4 <0.9.0;