我为什么找不到头文件iostream  程序如下：
#include <iostream>
using namespace std;

int main()
{
    bool check=trun;
    if(check==true)
    {
        cout<<"hello world\n";
    }
    return 0;
}
编译错误：
--------------------Configuration: 1 - Win32 Debug--------------------
Compiling...
1.cpp
d:\c语言学习\程序\1.cpp(1) : fatal error C1083: Cannot open include file: 'iostream': No such file or directory
Error executing cl.exe.

1.obj - 1 error(s), 0 warning(s)
求指教