Compilare: user.cpp: In function ‘int main()’: user.cpp:13:20: warning: suggest parentheses around ‘-’ inside ‘<<’ [-Wparentheses] a=(1<<n-1); ^ user.cpp:7:30: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("z.in","r",stdin); ^ user.cpp:8:32: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("z.out","w",stdout); ^