Created using remix-ide: Realtime Ethereum Contract Compiler and Runtime. Load this file by pasting this gists URL or ID at https://remix.ethereum.org/#version=soljson-v0.8.16+commit.07a7930e.js&optimize=false&runs=200&gist= Mapping explain in simple

contracts...mapping.sol

// SPDX-License-Identifier: GPL-3.0

pragma solidity >=0.7.0 <0.9.0;
import "hardhat/console.sol";

contract MappingCont {

//  Declare a mapiing
    mapping(address => uint) balances;
    // nested mapping
    mapping(address => mapping(address => bool)) approved;
    mapping(address => uint[]) scores;

    function foo(address sender) external {
         // Add value
    balances[msg.sender] = 100;
    // update map
    balances[msg.sender]=20;
    // get mapp
    balances[msg.sender];
    // Delete
    delete balances[msg.sender];
    // Default value
    // balances[someAddressDoNotExists]=0;

    // Exotic mapping a
    approved[msg.sender][sender] = true;
    approved[msg.sender][sender];
    console.log(approved[msg.sender][sender]);
    approved[msg.sender][sender]=false;
    delete approved[msg.sender][sender];
    
    // Exotic mapping b
    scores[msg.sender].push(1);
    scores[msg.sender].push(2);
    scores[msg.sender];
    scores[msg.sender][0]=10;
    delete scores[msg.sender][0];
    }
}