Compilare: main.c: In function 'main': main.c:63:8: warning: unused variable 'str' [-Wunused-variable] char *str; ^~~ main.c: In function '_generate_subsets': main.c:43:6: warning: ignoring return value of 'freopen', declared with attribute warn_unused_result [-Wunused-result] freopen("submultimi.out", "w", stdout); ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ main.c: In function 'main': main.c:67:5: warning: ignoring return value of 'freopen', declared with attribute warn_unused_result [-Wunused-result] freopen("submultimi.in", "r", stdin); ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ main.c:69:5: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result] scanf("%d",&len); ^~~~~~~~~~~~~~~~