Compilare: main.cpp: In function 'void buildPre(std::string)': main.cpp:15:11: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 15 | while(j < x.size()) { | ~~^~~~~~~~~~ main.cpp: In function 'int main()': main.cpp:37:27: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 37 | for(int i = x.size(); i <= x.size() + y.size(); i++) { | ~~^~~~~~~~~~~~~~~~~~~~~~ main.cpp:38:15: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 38 | if(pre[i] == x.size()) { | ~~~~~~~^~~~~~~~~~~