Main.cc:17:16: error: use of ‘auto’ in parameter declaration only available with -std=c++14 or -std=gnu++14 inline int mul(auto x, auto y) ^~~~ Main.cc:17:24: error: use of ‘auto’ in parameter declaration only available with -std=c++14 or -std=gnu++14 inline int mul(auto x, auto y) ^~~~