$ sudo apt-get update
$ sudo apt-get install g++-4.6 gcc-4.6 -y

$ sudo update-alternatives --remove-all gcc 
$ sudo update-alternatives --remove-all g++

$ sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-4.6 10
$ sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-4.2 20

$ sudo update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-4.6 10
$ sudo update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-4.2 20

$ sudo update-alternatives --install /usr/bin/cc cc /usr/bin/gcc 30
$ sudo update-alternatives --set cc /usr/bin/gcc

$ sudo update-alternatives --install /usr/bin/c++ c++ /usr/bin/g++ 30
$ sudo update-alternatives --set c++ /usr/bin/g++

$ sudo update-alternatives --config gcc
$ sudo update-alternatives --config g++

GCC, the GNU Compiler Collection

The GNU Compiler Collection includes front ends

for C, C++, Objective-C, Fortran, Ada, Go, and D,

as well as libraries for these languages (libstdc++)

GCC was originally written as the compiler for the GNU operating system.

The GNU system was developed to be 100% free software,

free in the sense that it respects the user's freedom.

We strive to provide regular,

high quality releases,

which we want to work well on a variety of native and cross targets

(including GNU/Linux)

and encourage everyone to contribute changes or help testing GCC.

Our sources are readily and freely available via Git and weekly snapshots.

Major decisions about GCC are made by the steering committee,

guided by the mission statement.

Please note that the following documentation refers to current development.

Some information may not be applicable to any existing release.

User-Level Documentation

GCC Installation Instructions

GCC Manual