Difference between Public vs Internal vs Private state variables in solidity programming langauge with example ?

Public state variables can be accessed internally as well as via messages. For a public state variable, an automatic getter function is generated.

 Internal state variables can be accessed only internally from the current contract or contract deriving from it without using this.

 Private state variables can be accessed only internally from the current contract they are defined not in the derived contract from it.

Example of  Public vs Internal vs Private state variables

pragma solidity ^0.5.0;

contract C {

   uint public data = 30;

   uint internal iData= 10;

   

   function x() public returns (uint) {

      data = 3; // internal access

      return data;

   }

}

contract Caller {

   C c = new C();

   function f() public view returns (uint) {

      return c.data(); //external access

   }

}

contract D is C {

   function y() public returns (uint) {

      iData = 3; // internal access

      return iData;

   }

   function getResult() public view returns(uint){

      uint a = 1; // local variable

      uint b = 2;

      uint result = a + b;

      return storedData; //access the state variable

   }

}