Does GCC have a GUI?
Plenty. Just to name a few, in no particular order:
Eclipse
KDevelop
Anjuta
MonoDevelop
Code::Blocks
Qt Creator
On Mac, Xcode
On Windows, Dev-C++
- Not real IDEs but still very popular development environments: Emacs, Vim
(As notnoop has noted, there is no official IDE but there are many standalone IDE applications that support targeting GCC)
No. gcc is a compiler! There are many IDEs that use gcc underneath the hood.
The choice of the IDE is dependent on the language you desire. For Objective-C, pretty much the only supported IDE is XCode on Mac OS X. XCode is bundled with Mac OS X (at least available for free online).
gcc is just a compiler, not an IDE.
On Windows you can use its MinGW port.
On Linux IDEs like emacs,vim,geany,code::blocks,netbeans use gcc as their compiler.
On Windows IDEs like Dev-Cpp, Code::Blocks, etc support MinGW port of gcc
EDIT :
ON Windows you can use Code::Blocks(my favourite) that comes bundled along with MinGW compiler or you can also use MSVC++ IDE(but I think it has a broken compiler :P)