Compilare: user.cpp: In function ‘void a_precalc()’: user.cpp:28:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(; j < a.size(); ) ^ user.cpp: In function ‘void str_match()’: user.cpp:51:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(j < b.size()) ^ user.cpp:61:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(i == a.size()) ^