Compilare: user.cpp: In function ‘bool solve(int, int, int)’: user.cpp:42:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] return stk.size() <= k; ^ user.cpp: In function ‘int main()’: user.cpp:76:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (k != stk.size() && !oki[i]) ^ user.cpp:47:40: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("salvare.in" , "r", stdin ); ^ user.cpp:48:40: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("salvare.out", "w", stdout); ^ user.cpp:51:27: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d %d", &n, &k); ^ user.cpp:55:31: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d %d", &x, &y); ^