I have c project which is written in linux. It runs on linux very well. But now I want to run it on windows. I want to know best and easy ways to run it on windows.
best way recompile it all using mingw compiler.
easy way recompile it under cygwin environment.
Elaborating a bit on the answers from caf and jartieda...
Cygwin is an attempt to emulate a (nearly) complete POSIX execution environment in a native Windows process. It is complete enough that a surprising amount of Unix application code simply compiles and runs using the familiar ./configure && make && make install
idiom. This trick was done by supplying a DLL that emulates POSIX system calls using the Windows API. Based on that, you get a complete GCC toolchain, bash, and all the usual command line utilities you are used to. One downside is that the compiled program is dependent on the Cygwin DLL, which makes it tricky to deliver the result to a system that does not already have Cygwin installed and whose user doesn't want to use a Unix shell.
MinGW is a port of the GCC toolchain that generates native Windows applications that depend on the well known (and distributed with Windows itself) MSVCRT.DLL C runtime library. It makes no attempt to emulate a POSIX operating system, but applications that are mostly based on the standard C libraries, will often build essentially unchanged.
MSYS is a compile-time environment that provides enough Unix utilities (including bash) to often allow ./configure
to run, and if the project supports the results, finish the build with MinGW's GCC. The result is a native Windows executable that does not depend on any DLLs you don't deliberately use aside from MSVCRT.DLL. Although the MSYS environment itself was a fork of an early version of the Cygwin project, it is primarily intended to be used to provide a unix-like place to compile native Windows applications: one would generally not build new applications based on its runtime environment.
Another approach to compiling for Windows is to use the MinGW cross compiler on linux. A number of MinGW's core developers work that way, testing they product either under Wine, or under Windows running in a VM or a separate PC.
If the program has a GUI component, then you may have additional difficulties. Some GUI frameworks are available for both Linux and Windows. Qt, wxWidgets, and IUP all leap to mind, but there are others out there.
Edit: I've improved the paragraph above about MSYS to emphasize that it is intended to be a compile-time environment for building programs that run as native Windows applications, and not a full POSIX environment like Cygwin.
Note, also, that there is always the option of porting the project to one of the more traditional compilers for Windows development. Open Watcom, the Borland compilers, and Microsoft all have free or inexpensive versions, although often enough not under licenses that make the opens source community entirely happy.
This approach probably requires more effort because the differences between a Linux environment and the Windows environment become more visible when you also switch from one toolchain to another. This is especially true of the Microsoft compilers which are historically not as fully standards compliant as GCC.
The answers you got so far, focus on installing the GNU operating system on the Windows kernel; but you could also use freeware tools from Microsoft. This solution is probably most attractive if you want to continue to develop on Linux, and only do a little work for porting on Windows:
Microsoft offers a simplified version of their development environment as freeware: Visual Studio Express (download). If your program does only file IO it will probably compile unmodified, because Microsoft supplies the C standard library too.
For GUI I also wholeheartedly recommend the Qt framework. It is very well written and documented; it is now licensed under the LGPL, so you can link it to proprietary applications without any cost. However it is written in C++ so you would need to change the programing language. For integration of QT with Visual Studio Express: I believe it works, but you need to try it out. About five years ago I tested the integration of (proprietary) QT and (professional) Visual Studio for my employer, and it worked perfectly.