ethereum-sc-example-1

Practical ethereum smart contract example

Function Structure

function (<parameter types>) {(visibility) internal|external}
[pure|constant|view|payable][returns (<return types>)]

Types

• bool: can be "true" or "false";
• int or int256: is an integer 256 bits signed;
• int8 to int256: from 8 to 8, is a signed integer with the referenced number of bits;
• uint or uint256: is an integer 256 bits unsigned;
• uint8 to uint256: from 8 to 8, is a unsigned integer with the referenced number of bits;
• address: 20 bytes of information referenced to an ethereum account (like an object);
  • balance: get account current balance;
  • transfer: account receives an amount;
  • call: is a low-level interface for sending a message to a contract. It returns false if the subcall encounters an exception, otherwise it returns true(use not recommended);
• string: text variable set between double quotes
• arrays: declare arrays with type or struct declaration before "[]". To get any value within an array you need to declare variable with an index. Ex:

uint[] value;

value[0];
value[1];
value[2];

• struct: definition of new types(similar to objects from classes, but always public atributes and no methods). Can be arrays or mappings. Ex:

struct Lottery {
  uint data;
  uint luckyNumber;
  address sender;
}
...
Lottery[] lotteries;
lotteries[0].luckyNumber = 1234;

• mappings: key x value type with an arbitrary key to reference an specific value. Ex:

mapping(address => uint) balances;

function update(uint balance) public {
  balances[msg.sender] = balance;
}

Ether Units

• wei: 1 == 1 wei;
• szabo(miliether): 1 == 1,000,000,000,000(1e12) wei;
• finney(microether): 1 == 1,000,000,000,000,000(1e15) wei;
• ether: 1 == 1,000,000,000,000,000,000(1e18) wei.

Time Units

• seconds: 1 == 1 seconds;
• minutes: 1 == 60 seconds;
• hours: 1 == 60 minutes;
• days: 1 == 24 hours;
• weeks: 1 == 7 days;
• years: 1 == 365 days
  • BEWARE: leap years.

Platform Properties

• block.blockhash(uint blockNumber) returns (bytes32): hash from a block;
• block.number(uint): actual block number;
• block.timestamp(uint) or now(uint): actual block timestamp(in seconds);
• gasleft() returns (uint256): lefting gas;
• msg.sender(address): account address that called the contract;
• msg.value(uint): amount of wei sent with the message.

Source	Data
Link	https://solidity.readthedocs.io/en/v0.4.25/units-and-global-variables.html#special-variables-and-functions

Visibility

• public/external
• private/internal

Modifiers

• constant/view: Use the global variable and access within the function only. Scope only within the function;
• pure: Only access local variable do not access the global variable;
• payable: Modify the global variable (or) rewritte the global variable. Scope outside function used.

Source

Source	Data
Author	ECOA PUCRIO
Instructor I	Rafael Nasser
Instructor II	Ronnie Paskin
Class	Contratos Inteligentes: Programação Solidity para Ethereum
Link	https://www.udemy.com/curso-completo-do-desenvolvedor-nodejs