I tried downoading 4.8 for 12.04 from https://launchpad.net/~ubuntu-toolchain-r/+archive/test/+packages (I did not find for 13.04 as is mentioned here: How to install gcc-4.8) and I think I messed up trying to install it.
apt-get install gcc-4.8 gives :
The following packages have unmet dependencies:
followed by a long list of packages and the recommendation:
E: Unmet dependencies. Try 'apt-get -f install' with no packages (or specify a solution)
apt-get -f install says
E: Error, pkgProblemResolver::Resolve generated breaks, this may be caused by held packages. E: Unable to correct dependencies
Please help I need it for the C++11 support
This was fixed with
sudo apt-get clean
sudo apt-get update
apt-get upgrade -f
Many thanks to everyone for trying to help!