I am a teacher\'s assistant for a C programming class, and the instructor uses Dev C++ as the compiler for the class. Personally I would use a different one, but the choice
I believe that Dev-C++ comes with a very old version of MinGW (3.4.x if I'm not mistaken). MinGW versions before 4.2.2 will have problems compiling programs on Windows Vista and later unless they are on the PATH.
So you can either update your version of MinGW (as you mentioned in a comment that you have already done), or you can add the MinGW\bin directory to the system path.