Compilare: user.cpp: In function ‘int main(int, const char**)’: user.cpp:101:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < b.size(); ++i) ^ user.cpp:105:43: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j = i + 1; j < b.size(); ++j) ^ user.cpp:135:35: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < b.size(); ++i) ^ user.cpp:139:47: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j = i + 1; j < b.size(); ++j) ^ user.cpp:170:33: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < sol.size(); ++i) ^ user.cpp:175:33: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < sol.size(); ++i) ^ user.cpp:52:37: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("magic2.in", "r", stdin); ^ user.cpp:53:39: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("magic2.out", "w", stdout); ^ user.cpp:55:20: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d", &n); ^ user.cpp:60:34: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d", &a[i][j]); ^