Smart Contract programming 101 with Solidity training used in Pizza Hackathon #0 Bangkok.

1. Training
nuuneoi

2. Agenda
• Introduction to Blockchain
• Introduction to Smart Contract Platform
• Smart Contract 101
• Coding with Solidity
• Deploy to Ethereum Network
• Work with Ethereum’s Smart Contract though web3
• Extras

3. Introduction to
Blockchain
nuuneoi

4. What is Blockchain? (Speedy Version)
“The Decentralized Database”

5. What is Blockchain? (Speedy Version)
“The Decentralized Database”

6. What is Blockchain? (Speedy Version)
“The Decentralized Database”

7. What is Blockchain? (Speedy Version)
“The Decentralized Database”

8. What is Blockchain? (Speedy Version)
“The Decentralized Database”

9. What is Blockchain? (Speedy Version)
“The Decentralized Database”

10. Introduction to
Smart Contract Platform
nuuneoi

11. What is Smart Contract Platform?
• Since Blockchain is the decentralized database. How about we let it keep the
“executable code” inside instead than just a simple transaction?

12. What is Smart Contract Platform?
• Everyone hold the same source code in the decentralized way.

13. How the code is executed?
• Same as the way transaction is made in Blockchain 1.0 we make a
transaction to call the code instead of making a money transferring tx.
• We call it “Blockchain 2.0”

14. What else Smart Contract could do?
• Store the variables (States)
• Transaction 1: a = 10
• Transaction 2: a = 20

15. Ethereum
nuuneoi

16. Ethereum Networks
Main Net
Network ID: 1
Consensus: PoW
Ropsten
Network ID: 3
Consensus: PoW
Client: Cross-Client
Rinkeby
Network ID: 4
Consensus: PoA
Client: Geth
Kovan
Network ID: 42
Consensus: PoA
Client: Parity
• Since the Ethereum is open sourced. There could be unlimited number of
networks out there and each of them are run separately.

17. Creating a Wallet
• Install MetaMask
• Chrome plugin

18. Faucet
• Get Ethereum for FREE! … (Sort of)
• https://faucet.kovan.network/ (Github account required)

19. Creating another Wallet
• Do it in MetaMask

20. Make the first transaction
• Let’s transfer some Ethereum from first account to the second one.
• Learn more a bit about Etherscan.

21. Smart Contract
Programming with
Solidity
nuuneoi

22. Ethereum Smart Contract
pragma solidity ^0.4.18;
contract SimpleContract {
uint balance;
constructor() public {
// Set initial balance as 1000
balance = 1000;
}
function setBalance(uint newBalance) public {
// Cap balance to be [0, 10000]
require(newBalance <= 10000);
// Set new balance
balance = newBalance;
}
function getBalance() public view returns(uint) {
return balance;
}
}

23. IDE: Remix
• https://remix.ethereum.org/

24. Solidity Helloworld
pragma solidity ^0.4.18;
contract SimpleContract {
uint balance;
constructor() public {
// Set initial balance as 1000
balance = 1000;
}
function setBalance(uint newBalance) public {
// Set new balance
balance = newBalance;
}
function getBalance() public view returns(uint) {
return balance;
}
}

25. Coding: Constructor
pragma solidity ^0.4.18;
contract SimpleContract {
uint balance;
constructor() public {
// Set initial balance as 1000
balance = 1000;
}
function setBalance(uint newBalance) public {
// Set new balance
balance = newBalance;
}
function getBalance() public view returns(uint) {
return balance;
}
}
constructor will be called
only once when deployed

26. Deploying
• Live Demo: Do it on remix

27. Working with Smart Contract through web3
• ABI
• BYTECODE

28. Working with Smart Contract through web3
• ABI
[ { "constant": false, "inputs": [ { "name": "newBalance", "type":
"uint256" } ], "name": "setBalance", "outputs": [], "payable": false,
"stateMutability": "nonpayable", "type": "function" }, { "inputs": [],
"payable": false, "stateMutability": "nonpayable", "type": "constructor" },
{ "constant": true, "inputs": [], "name": "getBalance", "outputs": [ {
"name": "", "type": "uint256" } ], "payable": false, "stateMutability":
"view", "type": "function" } ]
• BYTECODE
608060405234801561001057600080fd5b506103e860005560bf806100256000396000f3006
0806040526004361060485763ffffffff7c0100000000000000000000000000000000000000
00000000000000000060003504166312065fe08114604d578063fb1669ca146071575b60008
0fd5b348015605857600080fd5b50605f6088565b60408051918252519081900360200190f3
5b348015607c57600080fd5b506086600435608e565b005b60005490565b6000555600a1656
27a7a72305820cf77c0639acc98ef9acefd6386fe697d2d71d7478f3b9d459d8778557e3061
4a0029

29. Working with Smart Contract through web3
ABI

30. Working with Smart Contract through web3
• Live Coding: HTML + Javascript + jquery + web3.js + MetaMask
• Boilerplate: https://goo.gl/jychkY

31. Testing
$ npm install –g http-server
$ http-server .

32. Understand Gas Price
• See it on etherscan

33. Coding: Types
• Live Coding:
• bool
• int, uint, int8, uint8, int16, uint16, …, int256, uint256
• address
• fixed, ufixed
• byte, bytes
• string
• struct
• mapping
• enum
• []

34. Coding: Inheritance
• “is” contract A {
uint a;
function getA() public view returns(uint) {
return a;
}
}
contract B is A {
uint b;
function getBsumA() public view returns(uint) {
return b + a;
}
}

35. Coding: pure function
function func(uint x, uint y) public pure returns (uint) {
return x * (y + 42);
}

36. Coding: view function
uint a;
function func() public view returns (uint) {
return a;
}

37. Coding: pure & view function through read fn
uint a;
function func() public view returns (uint) {
return a;
}

38. Coding: pure & view function through read fn
uint a;
function func() public view returns (uint) {
return a;
}
function func2() public view returns (uint) {
return func();
}

39. Coding: pure & view function through write fn
uint a;
uint b;
function func() public view returns (uint) {
return a;
}
function func3(uint someVal) public returns (uint) {
b = someVal;
return func() + b;
}

40. Coding: require
function setBalance(uint newBalance) public {
// Check if newBalance is in [0, 10000]
require(newBalance <= 10000);
// Set new balance
balance = newBalance;
}

41. Coding: Visibility
• public – Can be either called internally or via messages.
• private – Only visible for the contract they are defined and
not in the derived contract.
• internal – Can only be accessed internally (i.e. from within
the current contract or contracts deriving from it)
• external - Can be called from other contracts and via
transactions. Cannot be called internally.

42. Coding: modifier
contract Ownable {
address public owner;
event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);
function Ownable() public {
owner = msg.sender;
}
modifier onlyOwner() {
require(msg.sender == owner);
_;
}
function transferOwnership(address newOwner) public onlyOwner {
require(newOwner != address(0));
emit OwnershipTransferred(owner, newOwner);
owner = newOwner;
}
}
https://goo.gl/ZLThph

43. Coding: modifier
pragma solidity ^0.4.18;
contract SimpleContract is Ownable {
uint balance;
constructor() public {
// Set initial balance as 1000
balance = 1000;
}
function setBalance(uint newBalance) public onlyOwner {
// Set new balance
balance = newBalance;
}
function getBalance() public view returns(uint) {
return balance;
}
}
contract Ownable {
address public owner;
event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);
function Ownable() public {
owner = msg.sender;
}
modifier onlyOwner() {
require(msg.sender == owner);
_;
}
function transferOwnership(address newOwner) public onlyOwner {
require(newOwner != address(0));
emit OwnershipTransferred(owner, newOwner);
owner = newOwner;
}
}
https://goo.gl/ZLThph

44. Coding: Events
pragma solidity ^0.4.18;
contract SimpleContract is Ownable {
event BalancedUpdated(uint balance);
uint balance;
constructor() public {
// Set initial balance as 1000
balance = 1000;
}
function setBalance(uint newBalance) public onlyOwner {
// Set new balance
balance = newBalance;
// Fire Event
emit BalanceUpdated(newBalance);
}
function getBalance() public view returns(uint) {
return balance;
}
}

45. Coding: Events
pragma solidity ^0.4.18;
contract SimpleContract is Ownable {
event BalancedUpdated(uint balance);
uint balance;
constructor() public {
// Set initial balance as 1000
balance = 1000;
}
function setBalance(uint newBalance) public onlyOwner {
// Set new balance
balance = newBalance;
// Fire Event
emit BalanceUpdated(newBalance);
}
function getBalance() public view returns(uint) {
return balance;
}
}
var event = SimpleContract.BalanceUpdated();
event.watch(function(error, result) {
// Will be called once there is new event emittted
});

46. Coding: payable
function register() public payable {
registeredAddresses[msg.sender] = true;
}

47. Redeploying
• Live Demo: See the difference [new contract address].
• Test the event.

48. Extras
nuuneoi

49. What is ERC-20?
// https://github.com/ethereum/EIPs/issues/20
interface ERC20Interface {
function totalSupply() public view returns (uint supply);
function balanceOf(address _owner) public view returns (uint balance);
function transfer(address _to, uint _value) public returns (bool success);
function transferFrom(address _from, address _to, uint _value) public returns (bool success);
function approve(address _spender, uint _value) public returns (bool success);
function allowance(address _owner, address _spender) public view returns (uint remaining);
function decimals() public view returns(uint digits);
event Approval(address indexed _owner, address indexed _spender, uint _value);
}
• ERC-20 is just a contract implemented the interface defined by ERC-20
standard.

50. Truffle: Solidity Framework
• Highly recommended
• Testable code
• Incremental deployment
• etc.

51. Store file on IPFS
• https://ipfs.io/
• Upload through Infura

52. Alternative Public Blockchain
• EOSIO: Smart Contract
• TomoChain: Smart Contract (Ethereum-Forked)
• NEM: Smart Contract
• Stellar: Payment (Non Turing Completed)

53. Create your own Smart Contract blockchain
• Hyperledger Fabric
• Use Golang to write Smart Contract