Compilare: main.c: In function 'main': main.c:154:5: warning: ignoring return value of 'freopen', declared with attribute warn_unused_result [-Wunused-result] freopen("apm.in", "r", stdin); ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~ main.c:155:5: warning: ignoring return value of 'freopen', declared with attribute warn_unused_result [-Wunused-result] freopen("apm.out", "w", stdout); ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ main.c:157:5: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result] scanf("%d %d", &n, &m); ^~~~~~~~~~~~~~~~~~~~~~ main.c:160:9: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result] scanf("%d %d %d", &u, &v, &w); ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~ At top level: main.c:57:12: warning: 'ecmp' defined but not used [-Wunused-function] static int ecmp(const void *a, const void *b) ^~~~ main.c:40:13: warning: 'opunion' defined but not used [-Wunused-function] static void opunion(int x, int y) ^~~~~~~ main.c:25:13: warning: 'make_set' defined but not used [-Wunused-function] static void make_set(int x) ^~~~~~~~