Compilare: user.cpp: In function ‘void adauga()’: user.cpp:22:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<s.size();++i) ~^~~~~~~~~ user.cpp: In function ‘void sterge()’: user.cpp:40:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<s.size();++i) ~^~~~~~~~~ user.cpp: In function ‘int aparitii()’: user.cpp:51:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<s.size();++i) ~^~~~~~~~~ user.cpp: In function ‘int prefix()’: user.cpp:62:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<s.size();++i) ~^~~~~~~~~