Compilare: user.cpp: In function ‘void back(int)’: user.cpp:38:11: warning: suggest explicit braces to avoid ambiguous ‘else’ [-Wparentheses] if(valid(k)) ^ user.cpp: In function ‘int main()’: user.cpp:48:38: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("combinari.in","r",stdin); ^ user.cpp:49:40: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("combinari.out","w",stdout); ^ user.cpp:50:24: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d%d",&N,&K); ^