Solidity ,Member“transfer”Not found or not visible after argument dependent lookup in address

Question

pragma solidity ^0.4.11;

/**
 * @title Ownable
 * @dev The Ownable contract has an owner address, and provides basic authorization control
 * functions, this simplifies the implementation of "user permissions".
 */
contract Ownable {

 address public owner;

    /**
   * @dev The Ownable constructor sets the original `owner` of the contract to the sender
   * account.
   */
  function Ownable() {
    owner = msg.sender;
  }


  /**
   * @dev Throws if called by any account other than the owner.
   */
  modifier onlyOwner() {
    (msg.sender == owner);
    _;
  }


  /**
   * @dev Allows the current owner to transfer control of the contract to a newOwner.
   * @param newOwner The address to transfer ownership to.
   */
  function transferOwnership(address newOwner) onlyOwner {
   (newOwner != address(0));      
    owner = newOwner;
  }

}

/**
 * @title Destructible
 * @dev Base contract that can be destroyed by owner. All funds in contract will be sent to the owner.
 */
contract Destructible is Ownable {

  function Destructible() payable { } 

  /**
   * @dev Transfers the current balance to the owner and terminates the contract. 
   */
  function destroy() onlyOwner {
    selfdestruct(owner);
  }

  function destroyAndSend(address _recipient) onlyOwner {
    selfdestruct(_recipient);
  }
}

contract BankAccount is Ownable, Destructible {

  function store() public payable {

  } 

  function withdraw(uint amount) public onlyOwner {
      if (this.balance >= amount) {
       msg.sender.transfer(amount);
     }
  } 
 }

Error message

browser/Ownable.sol:69:8: Error: Member "transfer" not found or not visible after argument-dependent lookup in address
       msg.sender.transfer(amount);
       ^-----------------^

Answer 1

in withdraw function, contract itself sends ether to msg.sender. so Include payable() modifier to the function when sending ether takesplace..

Answer 2

This:

pragma solidity ^0.4.11;

states that the compiler should be 0.4.11, or higher. This is ambiguous because ^ means "or higher". It's also a misleading way to express requirements because no one can know what breaking changes will unfold in the future.

Consider being specific, e.g. pragma solidity 0.4.11; The code compiles successfully in Remix with the compiler set to 0.4.11.

Your compiler will complain if it is not also version 0.4.11. Good. You want the code and the tooling to be aligned or you will always get strange errors.

Hope it helps.