Compilare: user.c: In function ‘main’: user.c:7:9: warning: ignoring return value of ‘freopen’, declared with attribute warn_unused_result [-Wunused-result] freopen("prefix.in","r",stdin),freopen("prefix.out","w",stdout),scanf("%d\n",&t); ^ user.c:7:40: warning: ignoring return value of ‘freopen’, declared with attribute warn_unused_result [-Wunused-result] freopen("prefix.in","r",stdin),freopen("prefix.out","w",stdout),scanf("%d\n",&t); ^ user.c:7:71: warning: ignoring return value of ‘scanf’, declared with attribute warn_unused_result [-Wunused-result] freopen("prefix.in","r",stdin),freopen("prefix.out","w",stdout),scanf("%d\n",&t); ^ user.c:9:7: warning: ignoring return value of ‘gets’, declared with attribute warn_unused_result [-Wunused-result] gets(s),k=p[1]=d=0,n=strlen(s); ^ /tmp/cczFqyOA.o: In function `main': user.c:(.text.startup+0x86): warning: the `gets' function is dangerous and should not be used.