Update:
Often people want the most recent version of gcc, and devtoolset is being kept up-to-date, so maybe you want devtoolset-N where N={4,5,6,7...}, check yum for the latest available on your system). Updated the cmds below for N=7.
There is a package for gcc-7.2.1 for devtoolset-7 as an example. First you need to enable the Software Collections, then it's available in devtoolset-7:
sudo yum install centos-release-scl
sudo yum install devtoolset-7-gcc*
scl enable devtoolset-7 bash
which gcc
gcc --version