linux系统下用gcc编译c++出错。初学者，请大家帮忙。

源代码是：
#include <iostream>
int main()
{float x;
int i;
x=3.6;
i=(int)x;
cout <<"x="<<x<<",i="<<i<< endl;
return 0;}

编译命令是：beibei@ubuntu:~/桌面$ gcc -Wall zeng.C -o zeng
可是出现下列错误：zeng.C:7: error: ‘cout’ was not declared in this scope
                               zeng.C:7: error: ‘endl’ was not declared in this scope

这是怎么个情况？？？？