G++ -I option for compiling program

Question

Here is a little problem that cannot be resolved by me such a Linux program newbie.

Now I have a main.cpp program which need to be compiled, there is a

#include "Down.h"

in the front of file.

Actually, this header file exist in the other directory, which locates at ../../../include directory. Besides, some other header files needed by Down.h also locate at this ../../../include directory.

Here is the problem, I compile main.cpp with command

g++ -I /../../../include main.cpp

However, it gives lots of error info which means it is not correct to be done like this.

Should I also change the include declaration into this one?

#include "../../../include/DownConvert.h"

May you please leave me with some advice? Thanks.

Edit:

After using g++ -I ../../../include main.cpp, I get the following errors:

$ g++ -I ../../../include main.cpp 

In file included from ../../../include/DownConvert.h:98,
from main.cpp:92: ../../../include/ResizeParameters.h:4:22: error:
TypeDefs.h: No such file or directory 

In file included from /usr/include/c++/4.4/bits/stl_algo.h:61, 
from /usr/include/c++/4.4/algorithm:62, 
from ../../../include/H2 

Solution

g++ -I /../../../include main.cpp

See that leading slash after the -I? That's an absolute path.
Change it to a relative path (shown below) and it'll work OK.

g++ -I ../../../include main.cpp