Compilare: main.cpp: In function 'void add(std::__cxx11::string)': main.cpp:18:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < s.size(); i++) { ~~^~~~~~~~~~ main.cpp: In function 'void del(int, int, std::__cxx11::string)': main.cpp:31:12: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(pos == s.size() - 1) { ~~~~^~~~~~~~~~~~~~~ main.cpp: In function 'int aps(std::__cxx11::string)': main.cpp:53:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < s.size(); i++) { ~~^~~~~~~~~~ main.cpp: In function 'int pre(std::__cxx11::string)': main.cpp:66:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < s.size(); i++) { ~~^~~~~~~~~~