address.transfer()
address.send()
address.call.value().gas()()

function transfer(address _address) public payable{

     _address.transfer(msg.value);

 }

  function transfer2(address _address) public payable{
     _address.transfer(10
 
 * 10**18);

 }

function transfer4(address _address) public payable {
       _address.send(10 ether);
 }

function transfer5(address _address) public payable returns(bool){
    return  _address.call.value(10
 
 ether)();
}

transfer與send相似，都為轉賬操作
transfer出錯丟擲異常
send、call出錯不丟擲異常，返回true或false
tansfer相對send更安全
send、call即便轉賬失敗也會執行其後的程式碼
慎用call函式轉賬，容易發生重入***。