Compilare: user.cpp: In function ‘void back(long long unsigned int, long long unsigned int)’: user.cpp:16:4: warning: suggest explicit braces to avoid ambiguous ‘else’ [-Wparentheses] if(k<=18) ^ user.cpp: In function ‘int main()’: user.cpp:31:35: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("multiplu.out","w",stdout); ^ user.cpp:32:33: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("multiplu.in","r",stdin); ^ user.cpp:33:24: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%llu%llu",&a,&b); ^