我用的是dev－c++
用#include<iostream.h>
时候报了一个警告：#warning This file includes at least one deprecated or antiquated header. \
Please consider using one of the 32 headers found in section 17.4.1.2 of the \
C++ standard. Examples include substituting the <X> header for the <X.h> \
header for C++ includes, or <iostream> instead of the deprecated header \
<iostream.h>. To disable this warning use -Wno-deprecated.

但是用#include<iostream>
又开始报cout没有声明！

怎么回事？