GCC 9.1.0 on Ubuntu 14.04 & 16.04 & 18.04:

sudo apt-get update -y && 
sudo apt-get upgrade -y && 
sudo apt-get dist-upgrade -y && 
sudo apt-get install build-essential software-properties-common -y && 
sudo add-apt-repository ppa:ubuntu-toolchain-r/test -y && 
sudo apt-get update -y && 
sudo apt-get install gcc-9 g++-9 -y && 
sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-9 60 --slave /usr/bin/g++ g++ /usr/bin/g++-9 && 
sudo update-alternatives --config gcc