Solidity programming

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pragma solidity ^0.6.0; // Any versions of 0.6.X will do.

contract SimpleStorage{

    uint256 public favouriteNumber; // This value will be initialised to 0

    //----Other types of variables----//
    // bool favouriteBool = true;
    // string favouriteString = "String";
    // int256 favouriteInt = -5;
    // address favouriteAddress = 0xBEB40F5Fd51b8E499Ec25Eae84227b65ea84563E;
    // bytes32 favouriteBytes = "cat"; // Strings can be converted to bytes

    // --- Visibility --- //
    // external - Can only be called by something outside of the contract
    // public - Anyone can call this value / function
    // internal - Can only be called by something inside of the contact, or any contracts deriving from it
    // private - Can only be called by within the contract, and NOT by any contacts deriving from it

    function store(uint256 _favouriteNumber) public {
        favouriteNumber = _favouriteNumber;
    }

    // --- view, pure --- //
    // `view`, `pure` do not cost any transactions.
    // They only access the variables, and they do not make any state changes
    // `view` lets you read a variable number
    // `pure` function lets you do maths operation 

    function retrieve() public view returns(uint256){
        return favouriteNumber;
    }

    // --- Struct --- //
    // Make your new data structure using struct!

    struct People {
        uint256 favouriteNumber;
        string name;
    }

    People public person = People({favouriteNumber: 777, name: "Hyunggi"});

    // --- Arrays --- //
    // People[] public people_dynamic_array;
    // People[2] public people_static_array;
    People[] public people;

    // --- mapping --- //
    // mapping - very similar to Python Dictionary. Hash table.
    mapping(string => uint256) public nameToFavouriteNumber;

    // --- memory vs storage --- //
    // memory - Data will only be wstored during the execution of the function
    // storage - Data will persist even after the execution

    function addPerson(string memory _name, uint256 _favouriteNumber) public{
        people.push(People(_favouriteNumber, _name));
        nameToFavouriteNumber[_name] = _favouriteNumber;
    }
}