Compilare: main.cpp: In function 'int main()': main.cpp:38:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int j = 0; j < h[i].size (); j++) { ~~^~~~~~~~~~~~~~ main.cpp:23:34: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen ("fft2d.in", "r", stdin); ^ main.cpp:24:36: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen ("fft2d.out", "w", stdout); ^