GNU gcc is available in /usr/bin/gcc. g++ is the C++ compiler based on gcc and is located in /usr/bin/g++. There are several additional versions of each of these (4.4, 4.6 and 4.8 found by adding -4.4, etc to the path).  GNU gcc 5.2 is installed in /lusr/opt/gcc-5.2.0.  If you need that version, you'll need to add /lusr/opt/gcc-5.2.0/bin to your path.