Compilare: user.c: In function ‘main’: user.c:9:11: warning: suggest explicit braces to avoid ambiguous ‘else’ [-Wparentheses] if(y>=0) ^ user.c:4:9: warning: ignoring return value of ‘freopen’, declared with attribute warn_unused_result [-Wunused-result] freopen("biti.in","r",stdin),freopen("biti.out","w",stdout),scanf("%d",&n),printf("%d\n",(k=(1<<n)+n-1)); ^ user.c:4:38: warning: ignoring return value of ‘freopen’, declared with attribute warn_unused_result [-Wunused-result] freopen("biti.in","r",stdin),freopen("biti.out","w",stdout),scanf("%d",&n),printf("%d\n",(k=(1<<n)+n-1)); ^ user.c:4:67: warning: ignoring return value of ‘scanf’, declared with attribute warn_unused_result [-Wunused-result] freopen("biti.in","r",stdin),freopen("biti.out","w",stdout),scanf("%d",&n),printf("%d\n",(k=(1<<n)+n-1)); ^