How to make C++ code Portable?

[siyuangao]

I am doing a group project that sometimes is going to be tested under Linux operating system but some function like
system("cls") only works on windows. I found a answer here says to use a header file:

// #define LINUX
// #define WINDOWS
// #define OSX

then add this in the source file

#ifdef LINUX
char os[] = "Linux";
#else
#ifdef WINDOWS
char os[] = "Windows";
#else
char os[] = "Mac OSX";
#endif
#endif

I just want to check if there a easier way to do, I am using GCC compiler.
Thank you.

[weaknessforcats]

The system() call should work in Linux but I believe the arguments to system() are OS dependent. That is, "cls" may only work on Windows and some things that work on Linux won't work on Windows.