Compilare: user.c: In function ‘main’: user.c:12:5: warning: implicit declaration of function ‘sqrt’ [-Wimplicit-function-declaration] for (i = 3; i <= sqrt(n); i += 2) ^ user.c:12:22: warning: incompatible implicit declaration of built-in function ‘sqrt’ [enabled by default] for (i = 3; i <= sqrt(n); i += 2) ^ user.c:9:12: warning: ignoring return value of ‘freopen’, declared with attribute warn_unused_result [-Wunused-result] freopen("ciur.in","r",stdin); ^ user.c:10:12: warning: ignoring return value of ‘freopen’, declared with attribute warn_unused_result [-Wunused-result] freopen("ciur.out","w",stdout); ^ user.c:11:10: warning: ignoring return value of ‘scanf’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d", &n); ^