Compilare: main.cpp: In function 'bool is_valid(int, int, int, std::vector<bool>&, std::vector<bool>&, std::vector<bool>&)': main.cpp:8:13: warning: suggest parentheses around '&&' within '||' [-Wparentheses] if (y <= n && columns[y] == true || diags1[n + x-y] == true || diags2[x+y] == true) ~~~~~~~^~~~~~~~~~~~~~~~~~~~~ main.cpp: In function 'int main()': main.cpp:15:35: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("damesah.in", "r", stdin); ^ main.cpp:16:37: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("damesah.out", "w", stdout); ^ main.cpp:19:17: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result] scanf("%d", &n); ^