Solidity Concepts:

• Flash Loans how they work Aave Docs
• Aave Protocol Flash Loans Deveoloper Docs

Solidity Language Reference:

• Function Modifiers like onlyOwner etc

• Using an interface to call functions from other contracts Cryptokittie Example

Solidity General

• Solidity Security

ERC20 Tokens

• Creating ERC20 Token OpenZeplin Docs

Get and set:

pragma solidity 0.7.5;

contract HelloWorld {

    int number;

    function getNumber() public view return(int) {
            return number;
    }

    function setNumber(int _number ) public {

        number = _number;
    }


}