The document provides a hands-on introduction to blockchain and smart contracts for software developers, focusing on Solidity data structures and ERC token standards. It covers setting up development tools, interacting with Ethereum's test networks, and creating an ERC20 coin contract. Detailed instructions are provided for deploying contracts and checking balances within the Ethereum ecosystem.

1. BLOCKCHAIN AND SMART
CONTRACTS SESSION 3
Hands-on introduction for
Software Developers and
Architects

2. PLAN FOR TODAY
Solidity data structures
Deep dive into the tool chain
Test networks
Very Simple Coin
ERC20 Token
ERC223 Token
ERC721 Token

3. SOLIDITY DATA
STRUCTURES
• Basic
• Arrays
• Structs
• Mappings

4. BASIC VALUE TYPES
Data Type Example
uint<M> , M=1,2,4, …, 256
int<M>, uint, int
Unsigned/signed integer uint256 counter = 1;
address 160-bit (20byte) value that
does not allow any
arithmetic operations. It is
suitable for storing
addresses of contracts or
keypairs belonging to
external persons.
Address has property
“balance”
address owner =
msg.sender;
If (owner.balance>10) …
bool Same as uint8 but values are
0 or 1
Bool b = 0;
b=true;
fixed<M>x<N>
ufixed<M>x<N>
Signed fixed-point decimal
number of M bits
fixed128x19 f = 1.1;

5. ARRAYS
Data Type Example
bytes1…bytes32, byte Fixed-size byte arrays byte1 bt1= 1;
Byte2 bt2=1;
if (bt2[0]==0) …
bt2.length
byte[N]
uint[N]
bool[N]
…
Fixed-size arrays byte[10] b;
fixed5x19[10] f;
byte[] Dynamic array uint[] memory a = new
uint[](7);
bytes Tightly-packed byte array bytes memory b = new
bytes(123);
string Same as bytes but can not string s=“Hello!”;

6. STRUCTS
pragma solidity ^0.4.11;
contract CrowdFunding {
// Defines a new type with two fields.
struct Funder {
address addr;
uint amount;
}
….
uint numFunders = 0;
mapping (uint => Funder) funders;
funders[numFunders++] = Funder({addr: msg.sender, amount: msg.value});
….
}

7. MAPPINGS
pragma solidity ^0.4.11;
contract CrowdFunding {
// Defines a new type with two fields.
struct Funder {
address addr;
uint amount;
}
….
uint numFunders = 0;
mapping (uint => Funder) funders;
funders[numFunders++] =
Funder({addr: msg.sender, amount: msg.value});
….
}
mapping(_KeyType => _ValueType)
_KeyType:
any type except mapping, dyn array,
contruct, enum or struct
_ValueType:
any type, including mappings

8. TOOLS
What you need to interact
with blockchain?
Setting up tools

9. TOOLBOX FOR ETHERIUM
Geth (command line tool)
Mist, Parity, Metamask (UI)
Etherscan.io

10. TEST BLOCKCHAINS
Ropsten
Rinkeby
Kovan

11. INSTALL PARITY
• sudo apt-get install openssl
libssl-dev libudev-dev
• bash <(curl
https://get.parity.io -kL)
Parity

12. (ALTERNATIVELY) INSTALL AND START LOCAL
TEST NETWORK
•$ npm install -g
ganache-cli
•$ ganache-cli &
Etherium
test
network

13. INSTALL NODE.JS
• sudo npm install npm@latest -gNODE.JS

14. INSTALL WEB3
• npm install web3
WEB3

15. INSTALL TRUFFLE FRAMEWORK
•$ sudo npm install -g truffle
•$ mkdir solidity-experiments
•$ cd solidity-experiments/
•$ truffle init
Truffle
Framework

16. INSTALL ZEPPELIN SOLIDITY
• sudo npm init -y
• sudo npm install -E
zeppelin-solidity
Zeppelin
Solidity

17. KOVAN TEST NETWORK
Connect to the network
Create account
Get some test Ether

18. KOVAN TESTNET
Kovan is a Proof of Authority publicly accessible blockchain for
Ethereum; created and maintained by a consortium of Ethereum
developers, to aide the Ethereum developer community.
Connect Get KETH Develop

19. START PARITY AND CONNECT TO
KOVAN
•sudo parity --chain
kovan ui
Etherium
with
Kovan

20. CREATE ACCOUNT ON KOVAN
NETWORK
parity account new --chain kovan
[Remember password and account id]
[Store password in a file for later use]

21. CONFIGURE TRUFFLE
• module.exports = {
• networks: {
• development: {
• host: "localhost",
• port: 8545,
• network_id: "*", // Match any
network id
• from: “<your account id>",
• gas: 4700000 // Gas limit}
• }
• };
Update
truffle.js

22. GET SOME ETHER (STEP 1, ASK)
Icarus Faucet (Automated after SMS
Verification)
https://youtu.be/99UucFzYCRc OR
Gitter Channel
https://gitter.im/kovan-testnet/faucet OR
Ask Gene – add comment with your account id
to the message board on
https://www.meetup.com/Blockchain-
Applications-and-Smart-
Contracts/events/tzwnjpyxfbmc/

23. GET SOME ETHER (STEP 2, SYNC
WITH NETWORK)
sudo parity --chain kovan

24. GET SOME ETHER (STEP 3, CHECK
YOUR BALANCE)
sudo geth attach
<path>/io.parity.ethereum/jsonrpc.ipc
account list
>
web3.fromWei(eth.getBalance(eth.coinbas
e), "ether")
50

25. SENDING ETHER
sudo geth attach
<path>/io.parity.ethereum/jsonrpc.ipc
account list
> eth.sendTransaction({from:sender,
to:receiver, value: amount})
>personal.unlockAccount(eth.coinbase)
>
eth.sendTransaction({from:eth.coinbase,
to:'0x00aA214a9Ecf3B4b7C3e70F8e7AB
CD39A71308E5', value: web3.toWei(1,

26. CREATE YOUR ERC20 COIN Code time

27. ERC20 TOKEN
Functions
totalSupply()
balanceOf(address tokenOwner)
allowance(address tokenOwner, address spender)
transfer(address to, uint tokens)
approve(address spender, uint tokens)
transferFrom(address from, address to, uint tokens)
Events
Transfer(address indexed from, address indexed to,
uint tokens);
Approval(address indexed tokenOwner, address
indexed spender, uint tokens);

28. CREATE ERC20 COIN CONTRACT
(SOLIDITY CODE)pragma solidity ^0.4.4;
import "../node_modules/zeppelin-solidity/contracts/token/StandardToken.sol";
/**
* @title RespectCoin
* @dev ERC20 Token example, where all tokens are pre-assigned to th
e creator.
* Note they can later distribute these tokens as they wish using `transfer` and
other
* `StandardToken` functions.
*/
contract RespectCoin is StandardToken {
string public constant name = "RespectCoin";
string public constant symbol = "RESPECT";
uint8 public constant decimals = 18;
uint256 public constant INITIAL_SUPPLY = 10000 * (10 ** uint256(decimals));
/**
* @dev Constructor gives msg.sender all tokens
*/
function RespectCoin() public {
totalSupply = INITIAL_SUPPLY;
balances[msg.sender] = INITIAL_SUPPLY;
}
}

29. CREATE DEPLOYMENT SCRIPT
var Respect =
artifacts.require("./RespectCoin.sol"
);
module.exports =
function(deployer) {
deployer.deploy(Respect);
};

30. DEPLOY CONTRACT TO THE TEST
NETWORK
$ truffle console
truffle(development)> truffle migrate --reset
Using network 'development'.
Running migration: 1_initial_migration.js
Deploying Migrations...
... 0xb6bbeaaf3649ecb38d548cba96f681682dad9e0225726924fbee3ce36eff94e3
Migrations: 0xc08c46796ba0edc0bebbbd0d90868c010055cb0e
Saving successful migration to network...
... 0x16fe364b9f2c3e8f07fa1ebd6b84b8ad9b4e750d8698a7e920d824ebd019dd80
Saving artifacts...
Running migration: 2_deploy_contracts.js
Deploying Hello...
... 0xfe120836b2d7395bd988104feff018fe352f93555f71003bbf1a64671cca9ba1
Hello: 0x2b649a87d20ce1ac3b6a0218e911165fa0f095f0
Saving successful migration to network...
... 0x1a09073a3b3f7996f3d63a81a99d8cd09198ad7b467f35f7ddc500a4291332b9
Saving artifacts...
truffle(development)>
truffle(development)> truffle migrate --reset

31. CHECK RESPECT BALANCE
truffle(development)> var RespectCoin =
RespectCoin.at(RespectCoin.address)
undefined
truffle(development)>
RespectCoin.balanceOf(web3.eth.accounts[0]).then(result =>
result.toString())
'1e+22'
truffle(development)>

32. LOOK AT RAW COMPILED CODE
truffle(development)>
web3.eth.getCode('0x228911363fa3ff0c99d98e8cdfa20aa4e
0c1db0a')'0x6060604052600436106100ba576000357c0100000000000000000000000000000000000000000000000000000000900463ffffffff16806306fdde03146100bf578063095ea7b31461014d57806318160ddd146101a757806323b872dd146101d05780632ff2e9dc14610249578063313ce56
71461027257806366188463146102a157806370a08231146102fb57806395d89b4114610348578063a9059cbb146103d6578063d73dd62314610430578063dd62ed3e1461048a575b600080fd5b34156100ca57600080fd5b6100d26104f6565b6040518080602001828103825283818151
815260200191508051906020019080838360005b838110156101125780820151818401526020810190506100f7565b50505050905090810190601f16801561013f5780820380516001836020036101000a031916815260200191505b509250505060405180910390f35b341561015857600
080fd5b61018d600480803573ffffffffffffffffffffffffffffffffffffffff1690602001909190803590602001909190505061052f565b604051808215151515815260200191505060405180910390f35b34156101b257600080fd5b6101ba610621565b6040518082815260200191505060405180910390
f35b34156101db57600080fd5b61022f600480803573ffffffffffffffffffffffffffffffffffffffff1690602001909190803573ffffffffffffffffffffffffffffffffffffffff16906020019091908035906020019091905050610627565b604051808215151515815260200191505060405180910390f35b3415610254576
00080fd5b61025c6109e6565b6040518082815260200191505060405180910390f35b341561027d57600080fd5b6102856109f5565b604051808260ff1660ff16815260200191505060405180910390f35b34156102ac57600080fd5b6102e1600480803573ffffffffffffffffffffffffffffffffffffffff169
060200190919080359060200190919050506109fa565b604051808215151515815260200191505060405180910390f35b341561030657600080fd5b610332600480803573ffffffffffffffffffffffffffffffffffffffff16906020019091905050610c8b565b604051808281526020019150506040518091
0390f35b341561035357600080fd5b61035b610cd4565b6040518080602001828103825283818151815260200191508051906020019080838360005b8381101561039b578082015181840152602081019050610380565b50505050905090810190601f1680156103c857808203805160018
36020036101000a031916815260200191505b509250505060405180910390f35b34156103e157600080fd5b610416600480803573ffffffffffffffffffffffffffffffffffffffff16906020019091908035906020019091905050610d0d565b604051808215151515815260200191505060405180910390f3
5b341561043b57600080fd5b610470600480803573ffffffffffffffffffffffffffffffffffffffff16906020019091908035906020019091905050610f31565b604051808215151515815260200191505060405180910390f35b341561049557600080fd5b6104e0600480803573fffffffffffffffffffffffffffffffffff
fffff1690602001909190803573ffffffffffffffffffffffffffffffffffffffff1690602001909190505061112d565b6040518082815260200191505060405180910390f35b6040805190810160405280600b81526020017f52657370656374436f696e00000000000000000000000000000000000000000081
525081565b600081600260003373ffffffffffffffffffffffffffffffffffffffff1673ffffffffffffffffffffffffffffffffffffffff16815260200190815260200160002060008573ffffffffffffffffffffffffffffffffffffffff1673ffffffffffffffffffffffffffffffffffffffff168152602001908152602001600020819055508273fffffffffffffffffffff
fffffffffffffffffff163373ffffffffffffffffffffffffffffffffffffffff167f8c5be1e5ebec7d5bd14f71427d1e84f3dd0314c0f7b2291e5b200ac8c7c3b925846040518082815260200191505060405180910390a36001905092915050565b60005481565b60008073ffffffffffffffffffffffffffffffffffffffff168373fffffff
fffffffffffffffffffffffffffffffff161415151561066457600080fd5b600160008573ffffffffffffffffffffffffffffffffffffffff1673ffffffffffffffffffffffffffffffffffffffff1681526020019081526020016000205482111515156106b257600080fd5b600260008573ffffffffffffffffffffffffffffffffffffffff1673fffffffffffffffffffffff
fffffffffffffffff16815260200190815260200160002060003373ffffffffffffffffffffffffffffffffffffffff1673ffffffffffffffffffffffffffffffffffffffff16815260200190815260200160002054821115151561073d57600080fd5b61078f82600160008773ffffffffffffffffffffffffffffffffffffffff1673fffffffffffffffffffffffffffff
fffffffffff168152602001908152602001600020546111b490919063ffffffff16565b600160008673ffffffffffffffffffffffffffffffffffffffff1673ffffffffffffffffffffffffffffffffffffffff1681526020019081526020016000208190555061082482600160008673ffffffffffffffffffffffffffffffffffffffff1673fffffffffffffffffff
fffffffffffffffffffff168152602001908152602001600020546111cd90919063ffffffff16565b600160008573ffffffffffffffffffffffffffffffffffffffff1673ffffffffffffffffffffffffffffffffffffffff168152602001908152602001600020819055506108f682600260008773ffffffffffffffffffffffffffffffffffffffff1673ffffffffff
ffffffffffffffffffffffffffffff16815260200190815260200160002060003373ffffffffffffffffffffffffffffffffffffffff1673ffffffffffffffffffffffffffffffffffffffff168152602001908152602001600020546111b490919063ffffffff16565b600260008673ffffffffffffffffffffffffffffffffffffffff1673fffffffffffffffffffffffffffffffff
fffffff16815260200190815260200160002060003373ffffffffffffffffffffffffffffffffffffffff1673ffffffffffffffffffffffffffffffffffffffff168152602001908152602001600020819055508273ffffffffffffffffffffffffffffffffffffffff168473ffffffffffffffffffffffffffffffffffffffff167fddf252ad1be2c89b69c2b068fc378daa
952ba7f163c4a11628f55a4df523b3ef846040518082815260200191505060405180910390a3600190509392505050565b601260ff16600a0a6127100281565b601281565b600080600260003373ffffffffffffffffffffffffffffffffffffffff1673ffffffffffffffffffffffffffffffffffffffff16815260200190815260
200160002060008573ffffffffffffffffffffffffffffffffffffffff1673ffffffffffffffffffffffffffffffffffffffff16815260200190815260200160002054905080831115610b0b576000600260003373ffffffffffffffffffffffffffffffffffffffff1673ffffffffffffffffffffffffffffffffffffffff16815260200190815260200160002060008
673ffffffffffffffffffffffffffffffffffffffff1673ffffffffffffffffffffffffffffffffffffffff16815260200190815260200160002081905550610b9f565b610b1e83826111b490919063ffffffff16565b600260003373ffffffffffffffffffffffffffffffffffffffff1673ffffffffffffffffffffffffffffffffffffffff16815260200190815260200
160002060008673ffffffffffffffffffffffffffffffffffffffff1673ffffffffffffffffffffffffffffffffffffffff168152602001908152602001600020819055505b8373ffffffffffffffffffffffffffffffffffffffff163373ffffffffffffffffffffffffffffffffffffffff167f8c5be1e5ebec7d5bd14f71427d1e84f3dd0314c0f7b2291e5b200ac8c7
c3b925600260003373ffffffffffffffffffffffffffffffffffffffff1673ffffffffffffffffffffffffffffffffffffffff16815260200190815260200160002060008873ffffffffffffffffffffffffffffffffffffffff1673ffffffffffffffffffffffffffffffffffffffff16815260200190815260200160002054604051808281526020019150506040518
0910390a3600191505092915050565b6000600160008373ffffffffffffffffffffffffffffffffffffffff1673ffffffffffffffffffffffffffffffffffffffff168152602001908152602001600020549050919050565b6040805190810160405280600781526020017f5245535045435400000000000000000000000000000
00000000000000000000081525081565b60008073ffffffffffffffffffffffffffffffffffffffff168373ffffffffffffffffffffffffffffffffffffffff1614151515610d4a57600080fd5b600160003373ffffffffffffffffffffffffffffffffffffffff1673ffffffffffffffffffffffffffffffffffffffff16815260200190815260200160002054821115
1515610d9857600080fd5b610dea82600160003373ffffffffffffffffffffffffffffffffffffffff1673ffffffffffffffffffffffffffffffffffffffff168152602001908152602001600020546111b490919063ffffffff16565b600160003373ffffffffffffffffffffffffffffffffffffffff1673ffffffffffffffffffffffffffffffffffffffff1681526020
0190815260200160002081905550610e7f82600160008673ffffffffffffffffffffffffffffffffffffffff1673ffffffffffffffffffffffffffffffffffffffff168152602001908152602001600020546111cd90919063ffffffff16565b600160008573ffffffffffffffffffffffffffffffffffffffff1673ffffffffffffffffffffffffffffffffffffffff1681
52602001908152602001600020819055508273ffffffffffffffffffffffffffffffffffffffff163373ffffffffffffffffffffffffffffffffffffffff167fddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef846040518082815260200191505060405180910390a36001905092915050565b60006
10fc282600260003373ffffffffffffffffffffffffffffffffffffffff1673ffffffffffffffffffffffffffffffffffffffff16815260200190815260200160002060008673ffffffffffffffffffffffffffffffffffffffff1673ffffffffffffffffffffffffffffffffffffffff168152602001908152602001600020546111cd90919063ffffffff16565b60026000
3373ffffffffffffffffffffffffffffffffffffffff1673ffffffffffffffffffffffffffffffffffffffff16815260200190815260200160002060008573ffffffffffffffffffffffffffffffffffffffff1673ffffffffffffffffffffffffffffffffffffffff168152602001908152602001600020819055508273ffffffffffffffffffffffffffffffffffffffff163373fffffffffff
fffffffffffffffffffffffffffff167f8c5be1e5ebec7d5bd14f71427d1e84f3dd0314c0f7b2291e5b200ac8c7c3b925600260003373ffffffffffffffffffffffffffffffffffffffff1673ffffffffffffffffffffffffffffffffffffffff16815260200190815260200160002060008773ffffffffffffffffffffffffffffffffffffffff1673fffffffffffffffffff
fffffffffffffffffffff168152602001908152602001600020546040518082815260200191505060405180910390a36001905092915050565b6000600260008473ffffffffffffffffffffffffffffffffffffffff1673ffffffffffffffffffffffffffffffffffffffff16815260200190815260200160002060008373fffffffffffffffffffff
fffffffffffffffffff1673ffffffffffffffffffffffffffffffffffffffff16815260200190815260200160002054905092915050565b60008282111515156111c257fe5b818303905092915050565b60008082840190508381101515156111e157fe5b80915050929150505600a165627a7a7230582025cadb1eada
4c612f0c8de847d597805ac8390d9d469e54a763a3ae1823274810029'

33. TOKENS
• ERC20
• ERC223
• ERC721

34. ERC223 TOKEN
ERC223 is backwards compatible with ERC20
merges the token transfer function among wallets and contracts into
one single function ‘transfer()’
does not allow token to be transferred to a contract that does not
allow token to be withdrawn

35. ERC223 TOKEN INTERFACE
contract ERC223 {
uint public totalSupply;
function balanceOf(address who) public view returns
(uint);
function name() public view returns (string _name);
function symbol() public view returns (string _symbol);
function decimals() public view returns (uint8 _decimals);
function totalSupply() public view returns (uint256
_supply);
function transfer(address to, uint value) public returns
(bool ok);
function transfer(address to, uint value, bytes data) public
returns (bool ok);
function transfer(address to, uint value, bytes data, string
custom_fallback) public returns (bool ok);
event Transfer(address indexed from, address indexed to,
uint value, bytes indexed data);

36. ERC721
People love collecting
Allow smart contracts to operate as tradable tokens
Each ERC721 is unique (non-fungible)
Support “ownership” functions
Each token is referenced by unique id
Tokens can have metadata (attributes)

37. ERC721
contract ERC721 {
event Transfer(address indexed _from, address
indexed _to, uint256 _tokenId);
event Approval(address indexed _owner, address
indexed _approved, uint256 _tokenId);
function balanceOf(address _owner) public view
returns (uint256 _balance);
function ownerOf(uint256 _tokenId) public view
returns (address _owner);
function transfer(address _to, uint256 _tokenId)
public;
function approve(address _to, uint256 _tokenId)
public;

38. STAY IN TOUCH
Gene Leybzon https://www.linkedin.com/in/leybzon/
https://www.meetup.com/members/90744
20/
https://www.leybzon.com