pragma solidity ^0.5.0;

contract C {

   uint public data = 30;

   uint internal iData= 10;

   function x() public returns (uint) {

      data = 3; // 内部访问

      return data;

   }

}

contract Caller {

   C c = new C();

   function f() public view returns (uint) {

      return c.data(); // 外部访问

   }

}

contract D is C {

   uint storedData; // 状态变量

   function y() public returns (uint) {

      iData = 3; // 派生合约内部访问

      return iData;

   }

   function getResult() public view returns(uint){

      uint a = 1; // 局部变量

      uint b = 2;

      uint result = a + b;

      return storedData; // 访问状态变量

   }

}