Compilare: user.cpp: In function ‘int main()’: user.cpp:28:67: warning: operation on ‘k’ may be undefined [-Wsequence-point] v[++ k] = mat[i][j] = (v[k - 2] * i + v[k - 1] * j + 1) % 10; ^ user.cpp:28:67: warning: operation on ‘k’ may be undefined [-Wsequence-point] user.cpp:34:28: warning: array subscript has type ‘char’ [-Wchar-subscripts] ++ fLine[i][mat[i][j]]; ^ user.cpp:35:27: warning: array subscript has type ‘char’ [-Wchar-subscripts] ++ fCol[i][mat[j][i]]; ^ user.cpp:16:36: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("qmatrix.in", "r", stdin); ^ user.cpp:17:38: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("qmatrix.out", "w", stdout); ^ user.cpp:20:41: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d %d %d %d\n", &N, &x, &y, &Q); ^ user.cpp:49:36: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%c %d %d\n", &q, &k, &p); ^