ERC20是以太坊上最受欢迎和广泛使用的代币标准之一。ERC20代币符合一组通用规则，包括代币的转账方法和余额查询方法。这些规则使得 ERC20 代币易于与钱包、交易所和其他合约进行集成和交互。

ERC20标准规定了代币合约必须实现以下6个函数：

1. balanceOf(address _owner)：获取给定地址的代币余额。

2. transfer(address _to, uint256 _value)：将代币从一个地址转移到另一个地址。

3. allowance(address _owner, address _spender)：返回给定地址的可转移余额。

4. approve(address _spender, uint256 _value)：允许另一个地址花费指定数量的代币。

5. transferFrom(address _from, address _to, uint256 _value)：从一个地址转移代币到另一个地址，前提是交易需要经过第三方的批准。

6. totalSupply()：获取代币的总供应量。

ERC20代币合约必须遵守并实现这些函数，以确保它们与其他代币和钱包兼容。此外，ERC20代币合约还必须包含代币的名称、符号和小数位数等元数据。

任何人都可以创建自己的ERC20代币，并将其用于支付、投票或其他用途。同时， ERC20代币也很容易与其他代币和钱包进行交互。

ERC20代币具有以下属性：

1. 总供应量（Total Supply）: 该代币发行的总数量。

2. 名称（Name）: 代币的名称，例如“以太币”。

3. 符号（Symbol）: 代币的简称，例如“ETH”。

4. 小数位数（Decimals）: 代币可以拆分的最小单位，例如“18”，代表代币可以被拆分为10的18次方的最小单位。

5. 余额（Balance）: 代币持有人的余额。

6. 转移记录（Transfer Record）: 代币的转移记录，包括发送、接收方、数量和时间。

7. 批准记录（Approval Record）: 代币的批准记录，包括批准者、受批准者和数量。

8. 总供应限制（Total Supply Limit）: 可以控制代币的总供应量，可以选择是否限制代币的总供应量。

以上属性可以在ERC20代币合约中进行定义和设置，以确保标准化和互操作性。

ERC721是一种以太坊上的代币标准，用于创建不可替代的代币。与ERC20代币不同，每个ERC721代币都是独一无二的，因此它们通常用于代表唯一的资产，如游戏中的虚拟物品、数字艺术品、房屋和土地证书等。

ERC721代币具有以下属性：

1. 每个ERC721代币都有一个独一无二的标识符（Token ID），通过这个标识符可以唯一地标识每个代币。

2. ERC721代币不可替代，即每个代币都是唯一的，不能被其他代币所替代。

3. 每个ERC721代币都可以被拥有者进行转移，就像普通的代币一样。

4. ERC721合约必须实现一组标准接口，包括balanceOf、ownerOf、approve、transferFrom和safeTransferFrom，以便于与其他合约进行交互和转移代币。

5. ERC721代币可以被继承和扩展，以实现更复杂的功能，例如用于游戏的虚拟物品。

下面是一个以太坊智能合约的示例代码，用于实现一个简单的ERC721代币合约：

pragma solidity ^0.8.0;contract MyNFT {// ERC721 标准string public constant name = "My NFT";string public constant symbol = "MYNFT";event Transfer(address indexed from, address indexed to, uint256 indexed tokenId);event Approval(address indexed owner, address indexed approved, uint256 indexed tokenId);mapping(uint256 => address) private _tokenOwner;mapping(uint256 => address) private _tokenApprovals;mapping(address => uint256) private _ownedTokensCount;function balanceOf(address owner) public view returns (uint256) {require(owner != address(0), "ERC721: balance query for the zero address");return _ownedTokensCount[owner];}function ownerOf(uint256 tokenId) public view returns (address) {address owner = _tokenOwner[tokenId];require(owner != address(0), "ERC721: owner query for nonexistent token");return owner;}function approve(address to, uint256 tokenId) public {address owner = ownerOf(tokenId);require(to != owner, "ERC721: approval to current owner");require(msg.sender == owner || isApprovedForAll(owner, msg.sender),"ERC721: approve caller is not owner nor approved for all");_tokenApprovals[tokenId] = to;emit Approval(owner, to, tokenId);}function getApproved(uint256 tokenId) public view returns (address) {require(_exists(tokenId), "ERC721: approved query for nonexistent token");return _tokenApprovals[tokenId];}function setApprovalForAll(address operator, bool approved) public {require(operator != msg.sender, "ERC721: approve to caller");_operatorApprovals[msg.sender][operator] = approved;emit ApprovalForAll(msg.sender, operator, approved);}function isApprovedForAll(address owner, address operator) public view returns (bool) {return _operatorApprovals[owner][operator];}function transferFrom(address from, address to, uint256 tokenId) public {require(_isApprovedOrOwner(msg.sender, tokenId), "ERC721: transfer caller is not owner nor approved");_transfer(from, to, tokenId);}function safeTransferFrom(address from, address to, uint256 tokenId) public {safeTransferFrom(from, to, tokenId, "");}function safeTransferFrom(address from, address to, uint256 tokenId, bytes memory _data) public {require(_isApprovedOrOwner(msg.sender, tokenId), "ERC721: transfer caller is not owner nor approved");_safeTransfer(from, to, tokenId, _data);}// 扩展功能function mint(address to, uint256 tokenId) public {require(to != address(0), "ERC721: mint to the zero address");require(!_exists(tokenId), "ERC721: token already minted");_tokenOwner[tokenId] = to;_ownedTokensCount[to] += 1;emit Transfer(address(0), to, tokenId);}function _exists(uint256 tokenId) internal view returns (bool) {address owner = _tokenOwner[tokenId];return owner != address(0);}function _isApprovedOrOwner(address spender, uint256 tokenId) internal view returns (bool) {require(_exists(tokenId), "ERC721: operator query for nonexistent token");address owner = ownerOf(tokenId);return (spender == owner || getApproved(tokenId) == spender || isApprovedForAll(owner, spender));}function _safeTransfer(address from, address to, uint256 tokenId, bytes memory _data) internal {_transfer(from, to, tokenId);require(_checkOnERC721Received(from, to, tokenId, _data), "ERC721: transfer to non ERC721Receiver implementer");}function _transfer(address from, address to, uint256 tokenId) internal {require(ownerOf(tokenId) == from, "ERC721: transfer of token that is not own");require(to != address(0), "ERC721: transfer to the zero address");_tokenApprovals[tokenId] = address(0);_ownedTokensCount[from] -= 1;_ownedTokensCount[to] += 1;_tokenOwner[tokenId] = to;emit Transfer(from, to, tokenId);}function _checkOnERC721Received(address from, address to, uint256 tokenId, bytes memory _data) internal returns (bool) {if (isContract(to)) {try IERC721Receiver(to).onERC721Received(msg.sender, from, tokenId, _data) returns (bytes4 retval) {return retval == IERC721Receiver(to).onERC721Received.selector;} catch (bytes memory reason) {if (reason.length == 0) {revert("ERC721: transfer to non ERC721Receiver implementer");} else {assembly {revert(add(32, reason), mload(reason))}}}} else {return true;}}function isContract(address account) internal view returns (bool) {uint256 size;assembly { size := extcodesize(account) }return size > 0;}
}interface IERC721Receiver {function onERC721Received(address operator,address from,uint256 tokenId,bytes calldata data) external returns (bytes4);
}

这个示例代码中包含了ERC721代币标准的主要功能，包括标识符、转移、批准、所有者等。此外，它还包括了一些扩展功能，例如 mint 函数用于发行新的代币。请注意，这个示例代码并不完整，你需要根据自己的需求进行修改和扩展。