This document provides an overview of creating a smart contract with Ethereum. It defines Ethereum as a blockchain platform that runs smart contracts, describes what smart contracts and Solidity are, and explains concepts like gas, gas price, and gas limit. It then outlines building a sample smart contract called PizzaFactory that allows users to pay for and deliver a pizza order. The document concludes by sharing resources for coding the first smart contract.

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Create your first Smart Contract with Ethereum
By Ricardo Aponte

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About me

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Agenda
What is Ethereum
What are Smart Contracts
What is Gas, Gas Limit and Gas Price
What are Denominations, Wei, Babbage, Lovelace, etc...
What is Solidity
Let’s Code our first Smart Contract!

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What is Ethereum
● Open-source, public, blockchain-based distributed computing platform that
runs Smart Contracts
● Applications (Smart Contracts) run exactly as programmed
● No possibilities of downtime, censorship, fraud or third-party interference
● Apps run on a custom blockchain
● Uses Ether as fuel for operating

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What is a Smart Contract
● Collection of Code (Functions) and Data (State)
● Resides at a specific address
● Pass messages between them
● Turing Complete
● Live on the blockchain in and EVM bytecode
● Written on a high level language such as Solidity

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Developer
Users

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What is Gas
Unit of measurement
Each operation has a cost
Analogy:
Electricity is measured by kilowatts per hour
Fuel like Gasoline and/or Diesel are measured in Gallons or Liters
Executing a Smart Contract is measured by Gas
Default: 21000 Gas

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Gas Price
The cost of unit of Gas the user is willing to pay
● With a car, it's $2.50 (price) per gallon (unit).
● With Ethereum, it's 20 GWEI (price) per gas (unit).
The costs:
● With a car, 10 gallons at $2.50 = $25
● With Ethereum, 21000 units of gas at 20 GWEI = 0.00042 ETH
The higher the Gas Price the more encouraged miners are to process your
transaction. https://ethgasstation.info/

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Gas Limit
● The maximum amount of units of gas you are willing to spend on a
transaction
● Prevents users from overly spending gas in a transaction
● All unused gas is refunded at the end of a transaction
● If not enough gas is specified to cover the computational resources you use
your transaction will fail due to an Out of Gas Error.

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What are Denominations
Ethereum is divisible by 18 decimal places and each one is a name tribute.
● Wei = 1 quintillionth (0.0000000000000000001) tribute to Wei Dai
● Babagge = 1 quadrillionth of (0.0000000000000001) tribute to Charles
Babagge
● Lovelace = 1 trillionth (0.0000000000001) tribute to Ada Lovelace
● Shannon = 1 billionth (0.0000000001) tribute to Claude Shannon
● Szabo = 1 millionth (0.0000001) tribute to Nick Szabo
● Finney = 1 thousandth (0.0001) tribute to Hal Finney

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What is Solidity
● Language similar to Javascript
● Allows to develop Smart Contracts
● Compiles to EVM bytecode
● Flagship language of Ethereum and most popular

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Solidity Concepts
Pragma
Contract (Class)
Data types (variables, scope)
● string
● uint
● map
● address
Functions
● public
● private
● internal
Global Object
● msg
Gas (The price you pay for the code you
execute) Anti-DoS
Naming conventions

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What we’ll code
The Problem:
● There is a group of people who want to eat pizza and want to pay for their
share
The Solution:
● Create a Smart Contract that will allow the group of people to pay for the
pizza and once the pizza is paid for, the pizza will be made and delivered

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Pizza Factory Smart Contract Flow
1. Define and store a Pizza Factory owner
2. Define a pizza name and price
3. Define storage for user payments
4. Create a Function to allow users to pay for pizza
5. Create a Function to transfer payment to owner in order to make the pizza
6. Challenge Round!

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Let’s Code our first Smart Contract
What we’ll use:
http://remix.ethereum.org/

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Other Resources
Complete Guide: http://solidity.readthedocs.io/en/latest/
Style Guide: http://solidity.readthedocs.io/en/develop/style-guide.html
Security Considerations: http://solidity.readthedocs.io/en/develop/security-
considerations.html
OpenZeppelin: https://github.com/OpenZeppelin
CryptoZombies: https://cryptozombies.io/

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PizzaPlace.sol
pragma solidity ^0.4.19;
contract PizzaPrice {
// Define owner
// Define Payment information
// Initialize Contract
// Define Pizza name and value in wei
// Define Users
// Pay for Pizza
// Make Pizza
}