Compilare: user.cpp: In function ‘int main()’: user.cpp:40:43: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(;a < s[i].size(); ++a) ^ user.cpp:42:48: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(b < s[j].size() && s[j][b] != s[i][a]) b++; ^ user.cpp:43:47: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (b == s[j].size()) break; ^ user.cpp:46:43: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (a == s[i].size()) ^ user.cpp:38:28: warning: unused variable ‘ok’ [-Wunused-variable] int ok = 0; ^