Change default gcc /g++/ cpp version used in ubuntu

update_gcc.sh

# for advanced users only
# sudo add-apt-repository ppa:ubuntu-toolchain-r/test
GCC_VERSION=11 # or whatever
sudo apt update
sudo apt install gcc-${GCC_VERSION} gcc-${GCC_VERSION}-locales gcc-${GCC_VERSION}-multilib g++-${GCC_VERSION} g++-${GCC_VERSION}-multilib cpp-${GCC_VERSION}
sudo update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-${GCC_VERSION} 10
# test with
g++-${GCC_VERSION} --version
sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-${GCC_VERSION} 10
# test with
gcc-${GCC_VERSION} --version
sudo update-alternatives --install /usr/bin/cpp cpp /usr/bin/cpp-${GCC_VERSION} 10
# test with
cpp-${GCC_VERSION} --version

# revert with
# sudo update-alternatives --config g++
# sudo update-alternatives --config gcc
# sudo update-alternatives --config cpp