8 位的 keccak

# Guess the random number

In short  now  is just an alias for  block.timestamp

block.blockhash()  is now  blockhash()  and  now  is  block.timestamp . We’ll see this further on.

timestamp 和 block 信息都在区块链探索器上可见

timestamp Epoch Converter - Unix Timestamp Converter

Capture Ether: Guess the Random Number on a Smart Contract | by Tomás | Better Programming

# Guess the new number

payable(msg.sender).transfer(address(this).balance);

# Predict the block hash

The block hashes are not available for all blocks for scalability reasons.
You can only access the hashes of the most recent 256 blocks, all other values will be zero.