# Udemy-Ethereum and Solidity-Section 1 Notes

**Published by:** [sunnyxuan](https://paragraph.com/@sunnyxuan/)
**Published on:** 2022-11-24
**URL:** https://paragraph.com/@sunnyxuan/udemy-ethereum-and-solidity-section-1-notes

## Content

While browsing crypto experts’ LinkedIn profiles, I found this course👇 https://www.udemy.com/course/ethereum-and-solidity-the-complete-developers-guide/ This course aims to teach you how to build web apps with Ethereum. I’m not a geek and haven’t even built a website or app before, but learning some underlying technologies of Web3 can help me better understand this ecosystem. It's important to review what you've learned in stages, so I’ll take some notes whenever I finish a section. Here are the notes from Section One. History 2018.10.31 Bitcoin was born, a peer-to-peer electronic cash system The most important part of the Ethereum network: SMART CONTRACT(a piece of code that lives in the Ethereum blockchain) What is Ethereum Working with Ethereum = Working with a network of computers There are many different Ethereum networks: one main Ethereum networks test networks-solely for testing code & transactions Networks are formed by one or more nodes(a node is a machine that runs an Ethereum client) Anyone can run a node Each node we create has a full & separate copy of the blockchain Interfacing with Ethereum networks For developers: web3.js (portal into the Ethereum network) For consumers: Metamask; Mist Browser - What it means to have an account: account address, public key, private key What’s a transaction? Click submit on the form👉address sent to the backend server👉backend server uses Web3 library to create a transaction object👉backend server sends the transaction object to the goerli network👉backend server waits for the transaction to be confirmed👉backend server sends a success message back to the browser Nonce: How many times sender has sent a transaction Value: Amount of ethers sent gasPrice: Amount of ethers the sender is willing to pay per unit of gas to get this transaction processed startGas/gasLimit: Units of gas that this transaction can consume v/r/s: Cryptographic data can be used to generate the sender’s account address. Generated from the sender’s private key. Q: Why is blockchain so hard to understand? It has to solve an incredibly difficult problem: the representation and transfer of millions, billions, and trillions of dollars between people. Why do we have to wait?-Mining The whole process of mining Block time A few clarifications on Ander’s video: “Looking for a hash that starts with some number of leading zeroes” should be “a hash that is less than some target value.” [Block Time]The amount of time to run different possible hashes until we find the final value. Solidity contract definition (solidity)👉solidity compiler👉Byte code(deploy in Ethereum) 👉Application Binary Interface(ABI) Code pragma solidity ^0.4.17; contract Inbox { string public message; function Inbox(string initialMessage) public { message = initialMessage; } function setMessage(string newMessage) public { message = newMessage; } function getMessage() public view returns (string) { return message; } } Function declarations function getMessage() public view returns (string) { ☝function name ☝function type☝return type Common function types Public: Anyone can call this function (who has Ethereum account) Private: Only this contract can call this function View/Constant: This function returns data and doesn’t modify the contract’s data Pure: Function will not modify or even read the contract’s data Payable: Might attempt to call it or send money to the contract Testing with Remix Contract source (remix editor)👉compilation to bytecode👉deployment👉In-browser fake network(inbox instance) Running functions Anytime we want to change any data that gets stored on the blockchain, we have to submit a transaction Calling a function Cannot modify the contract’s data Can return data Runs instantly(doesn’t need transaction) free to do Sending a transaction to a function Can modify data Returns the transaction hash Takes time to execute costs money Wei VS Ether 1 dollar=100 cents 1 ether=1,000,000,000,000,000,000 Wei Mnemonic phrases 12-word mnemonic👉BIP39 mnemonic algorithm👉account 1: Consuming; account 2: Saving; account 3: Business…

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