View Compilation Error

0_0_38537265_13055.cpp: In function 'constexpr ull qpow(ull, ull, int)':
0_0_38537265_13055.cpp:59:1: error: body of constexpr function 'constexpr ull qpow(ull, ull, int)' not a return-statement
 }
 ^
0_0_38537265_13055.cpp: At global scope:
0_0_38537265_13055.cpp:61:10: error: 'in' function uses 'auto' type specifier without trailing return type
 auto& in() { return (std::cin); }
          ^
0_0_38537265_13055.cpp:61:10: note: deduced return type only available with -std=c++1y or -std=gnu++1y
0_0_38537265_13055.cpp:63:33: error: 'in' function uses 'auto' type specifier without trailing return type
 auto& in(T& first, Args&... args) { std::cin >> first; return in(args...); }
                                 ^
0_0_38537265_13055.cpp:63:33: note: deduced return type only available with -std=c++1y or -std=gnu++1y