Compilare: user.c: In function ‘sieve’: user.c:33:9: warning: implicit declaration of function ‘exit’ [-Wimplicit-function-declaration] exit(0); ^ user.c:33:9: warning: incompatible implicit declaration of built-in function ‘exit’ [enabled by default] user.c:31:16: warning: ignoring return value of ‘freopen’, declared with attribute warn_unused_result [-Wunused-result] freopen("prim.out", "w", stdout); ^ user.c: In function ‘main’: user.c:48:9: warning: ignoring return value of ‘fscanf’, declared with attribute warn_unused_result [-Wunused-result] fscanf(f, "%d", &K); ^