Compilare: user.cpp: In function ‘int main()’: user.cpp:91:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i=0; i<ans.size(); i++) ^ user.cpp:68:35: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen ("algebra.in", "r", stdin); ^ user.cpp:69:37: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen ("algebra.out", "w", stdout); ^ user.cpp:70:17: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf ("%d", &n); ^ user.cpp:73:32: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf ("%lf", &A[i][j]); ^