Compilare: user.c: In function ‘main’: user.c:68:16: warning: format ‘%lu’ expects argument of type ‘long unsigned int’, but argument 2 has type ‘size_t {aka unsigned int}’ [-Wformat=] printf("%lu\n", i); ^ user.c:31:5: warning: ignoring return value of ‘freopen’, declared with attribute warn_unused_result [-Wunused-result] freopen("prefix.in", "r", stdin); ^ user.c:32:5: warning: ignoring return value of ‘freopen’, declared with attribute warn_unused_result [-Wunused-result] freopen("prefix.out", "w", stdout); ^ user.c:34:5: warning: ignoring return value of ‘read’, declared with attribute warn_unused_result [-Wunused-result] read(0, buf, CHUNK); ^