（32 小时最全课程）区块链，智能合约 & 全栈 Web3 开发
# Full BlockChain Solidity Learning
## Chapter #1
### Calculate Transaction Fee
Transaction Fee = ( Block Base Fee Per Gas + MaxPriorityFee Per Gas ) \* Gas Used
- Base Fee: The minimum "gas price" to send your transaction
- 1 Eth = 1000000000 GWei = 1000000000000000000 Wei
### Consensus
Consensus is the mechanism used to agree on the state of a blockchain.
#### 1. Chain Selection Algorithm
#### 2. Sybil Resistance Mechanism
- Like PoW(Proof of Work) and PoS(Proof of Stake)
## Chapter #2
### First Contract in Remix
```sol
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.7;
// This is a smart contract
contract SimpleStorage {
// The basic types: boolean | unit | int | address | bytes
// unit: POSITIVE number only
bool hasFavoriteNumber = true;
uint favoriteNumber = 123;
string favoriteNumberInText = 'five';
bytes favoriteBytes = 'cat';
}
```
> Default Value
> `uint favoriteNumber; // 0`
### Function
```sol
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.7;
// Contract: 0xd9145CCE52D386f254917e481eB44e9943F39138
contract SimpleStorage {
uint256 favoriteNumber;
function store(uint256 _favoriteNumber) public {
favoriteNumber = _favoriteNumber;
}
// getter function of favoriteNumber
function retrieve() public view returns(uint256) {
return favoriteNumber;
}
}
```
> **Tips:**
>
> - Smart Contracts have addresses just like our wallet accounts do.
> - Any time you change something on-chain, including making a new contract, it happens in a transaction.(部署合约其实就是在发送一个交易；我们在区块链上做任何事情，修改任何状态，其实就是在发送一个交易)
> - `view, pure`: 标记上后不会花费 gas，因为这意味着我们只会读取这个合约的状态（除非你在要花费 gas 的 store 函数中调用它）
> - `view and pure` functions disallow modification of state.(我们不可以在这个函数里修改任何状态)
#### Function Visibility Specifiers
- public: it creates `getter()` automatically.
- private: only visible in current contract.(此合约可见)
- external: only visible externally.(合约外部可见，合约外的账户可以调用这个函数)
- internal(default visibility ): only visible internally.(合约内部可见，这有这个合约或者继承它的合约可以调取)
### Arrays and Structure
We want to store different people with different numbers here. So we are using `struct`.
```sol
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.7;
// Contract: 0xd9145CCE52D386f254917e481eB44e9943F39138
contract SimpleStorage {
uint256 public favoriteNumber;
// Instantiate a person
People public person = People({favoriteNumber: 12, name: 'Logic'});
struct People {
uint256 favoriteNumber;
string name;
}
function store(uint256 _favoriteNumber) public {
favoriteNumber = _favoriteNumber;
}
// getter function of favoriteNumber
function retrieve() public view returns(uint256) {
return favoriteNumber;
}
}
```
We are storing the structures as an array here
```sol
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.7;
// Contract: 0xd9145CCE52D386f254917e481eB44e9943F39138
contract SimpleStorage {
uint256 public favoriteNumber;
struct People {
uint256 favoriteNumber;
string name;
}
// 这里用people数组来存储多个`struct`的实例`People`
People[] public people;
// Add `people` function
function addPerson(string memory _name, uint256 _favoriteNumber) public {
People memory newPerson = People({favoriteNumber: _favoriteNumber, name: _name});
// People memory newPerson = People(_favoriteNumber, _name);
people.push(newPerson);
}
function store(uint256 _favoriteNumber) public {
favoriteNumber = _favoriteNumber;
}
// getter function of favoriteNumber
function retrieve() public view returns(uint256) {
return favoriteNumber;
}
}
```
> - 创建了 people 数组，编制后会有一个`people`的按钮，这里可以输入`index`来找到对应的 structure；
> - 同时，这里还写了`addPerson`函数来添加 structure 到 array 中；
> - `memory`是一种 solidity 的存储方式，这里表示的是临时存储，函数执行完毕后数据会被清除。
### Memory, Storage and Calldata
EVM can access and store information in six places:
1. Stack
2. Memory: 可以被修改的临时变量
3. Storage: 可以被修改的永久变量
4. Calldata: 不能被修改的临时变量
5. Code
6. Logs
> Data location can only be specified for `array`, `struct` or `mapping` types
> `string` type actually is a `bytes` type
### Mappings
A mapping is a data structure where a key is "mapped" to a single value.
```sol
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.7;
// Contract: 0xd9145CCE52D386f254917e481eB44e9943F39138
contract SimpleStorage {
uint256 public favoriteNumber;
mapping(string => uint256) public nameToFavoriteNumber;
// Add `people` function
function addPerson(string memory _name, uint256 _favoriteNumber) public {
nameToFavoriteNumber[_name] = _favoriteNumber;
}
}
```
