coding practice

[x] Hello World

• contract structure:
  • spdx license identifier by open-zeppelin
  • pragma statement: solidity version
  • contract

[x] First App

• simple app that counts:
  • increments(+=) & decrement(-=)
  • gets current count

[x] Primitive Data Types

• data types
  • bool
    • true/false
  • unit: only has positive integers
    • int range: 0 to 2**256-1
  • int: has both negative & positive integers:
    • int range: -2 ** 256 -1 to 2**256-1
  • dynamically-sized byte arrays

[x] Variables

• state variables: saved on the blockchain: declared
• local state: not saved on the blockchain
• global state: accessible from the blockchain e.g timestamp, msg.sender

[x] Constants

• hard-coding constants using upper-case that can’t be modified to save gas costs

[x] Immutable

• hardcoding immutable and setting them to the constructor: no modifications

[x] Reading and Writing to a State Variable

• reading state variable without sending transaction
• writing to state variable by sending a transaction

[x] Ether and Wei

• units of Ether i.e one ether equal to 10 ** 18 Wei

[x] Gas and Gas Price

• gas is the amount of Ether you need for a transaction
  • gas - computational unit
  • gas price - the amount of Ether willing to pay per gas spent
  • the transaction with a higher gas price - has a high priority to be included in the block
  • unspent gas is refunded
  • if all gas is used transaction might fail and its state changes to undone and gas that has been spent isn’t refunded

[x] If / Else

• using if & else loops with return statements for all checks

[x] For and While Loop

• for loop: good for dynamic arrays & undetermined data —- a good option
• while loop: for deterministic data its a slave option

[x] Mapping

mapping(keyType => valueType)

• keyType could be a built-in value type, bytes, string, or any contract while value type could be any type or even another mapping or array.
  • mapping returns a value if it wasn’t set it will return a default value
  • mapping value can be updated
  • mapping value can be deleted back to its default value
• nested mapping

mapping(address => mapping(uint => bool)) public nested;

• can get the value of nested mapping even if it wasn't initialized

[x] Array

• Arrays can have compile-time fixed/dynamic size
• fixed arrays all their elements initialize to zero

unit[10] public myFixedSizeArr

• array methods in solidity:
  • getArray: get all elements of the array
  • push: increase the length by one
  • pop: remove last element of the array
  • remove: delete an element of an array but it will be returned to 0/default
  • getLength: get the actual length of array/ number of array elements
  • create array elements in memory: only fixed-size arrays can be created not dynamic
• Array methods: shift, push, pop, length, delete, checking index

[x] Enum

• solidity supports enumerables & they’re useful to model choice & keep the track safe. They’re declared outside a contract and imported to the contract.
• the first element is the default element listed

[x] Structs

• define your own type by creating a struct. It's useful for grouping related data together. Can be declared outside a contract & imported
  • initializing struct by:
    • calling it like a function
    • key-value mapping
    • initialize empty struct then update it

[x] Data Locations - Storage, Memory, and Call data

variables used to declare or explicitly specify data location are memory, calldata, or storage.

• storage: its a state variable(stored on the blockchain)
• memory: exists while the function is called locally
• calldata” special data location that contains function arguments

[x] Function

there are several ways to return outputs from a function