Compilare: user.cpp: In function ‘void det_mat()’: user.cpp:30:15: warning: variable ‘k’ set but not used [-Wunused-but-set-variable] int i, j, k, a, b, p; ^ user.cpp: In function ‘void read()’: user.cpp:10:38: 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:11:43: 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: In function ‘void write()’: user.cpp:64:40: 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:67:41: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%c %d %d\n", &ch, &k, &p); ^