Compilare: user.cpp: In function ‘int main()’: user.cpp:77:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0 ; i < S.size() ; ++ i) { ^ user.cpp:79:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(i + 1 < S.size() && S[i].first == S[i + 1].first) { ^ user.cpp:50:32: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen(infile, "r", stdin); ^ user.cpp:51:26: warning: ignoring return value of ‘char* fgets(char*, int, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] fgets(s, MAXN, stdin); ^