Linux-Switch-gcc-g++-version

• Install the version you want to use
  $sudo apt-get install gcc-x.x
• Add this version into the list, make a priority, following example make the priority 100
  $sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-x.x 100
  $sudo update-alternatives --config gcc
• If it already had more than one version in the list, then it will notify you the version, and you chould switch version between them
• Use the above step to switch g++ version