Compilare: user.c: In function ‘main’: user.c:5:12: warning: ignoring return value of ‘freopen’, declared with attribute warn_unused_result [-Wunused-result] freopen("cal.in","r",stdin),freopen("cal.out","w",stdout),scanf("%d%d%d%d",&a,&b,&s,&n); ^ user.c:5:40: warning: ignoring return value of ‘freopen’, declared with attribute warn_unused_result [-Wunused-result] freopen("cal.in","r",stdin),freopen("cal.out","w",stdout),scanf("%d%d%d%d",&a,&b,&s,&n); ^ user.c:5:68: warning: ignoring return value of ‘scanf’, declared with attribute warn_unused_result [-Wunused-result] freopen("cal.in","r",stdin),freopen("cal.out","w",stdout),scanf("%d%d%d%d",&a,&b,&s,&n); ^ user.c:7:14: warning: ignoring return value of ‘scanf’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d%d",&c,&d); ^