Compilare: main.c: In function '_union': main.c:28:8: warning: suggest explicit braces to avoid ambiguous 'else' [-Wparentheses] if (x!=y) ^ main.c: In function 'main': main.c:43:9: warning: variable 'n' set but not used [-Wunused-but-set-variable] int n, m; ^ main.c:40:5: warning: ignoring return value of 'freopen', declared with attribute warn_unused_result [-Wunused-result] freopen("disjoint.in", "r", stdin); ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ main.c:41:5: warning: ignoring return value of 'freopen', declared with attribute warn_unused_result [-Wunused-result] freopen("disjoint.out", "w", stdout); ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~