It will be handy to have a C compiler which is ready to be used without installing.Mingw is the windows version of the open source gcc compiler suite. It can be used to compile both C and C++. It is possible to use the Mingw from one pc to another by copying the C:\Mingw folder, but there is some problem regarding the folder path settings and update functionality.
Portable mingw from portableapps.com is a portable version of mingw compiler which contains batch scripts to invoke the commandline with the environment variables set and also has an update batch script. Previous versions of this package even has the msys environment.
Here I have uploaded my copy of Mingw Portable installation. In which the larger file is an older version, but contains msys.