rentAFlat

function rentAFlat(uint8 _flat) public payable returns(uint256) {
    tenantAddress = msg.sender;
    if (msg.value % flatDB[_flat].priceInWei == 0 && msg.value > 0 && flatDB[_flat].flatIsAvailable == true) {
        uint256 numberOfNightsPaid = msg.value / flatDB[_flat].priceInWei;
        flatDB[_flat].flatIsAvailable = false;
        flatDB[_flat].currentOccupant = tenantAddress;
        landlordAddress.transfer(msg.value);
        return numberOfNightsPaid;
    } else {
        tenantAddress.transfer(msg.value);
        return 0;
    }
}