Compilare: main.cpp: In function 'int main()': main.cpp:75:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (ptr < mat.size() && mat[ptr][0] < mat[ aux[i].first ][0]) ~~~~^~~~~~~~~~~~ main.cpp:32:36: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("engineer.in", "r", stdin); ^ main.cpp:33:38: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("engineer.out", "w", stdout); ^