View Compilation Error

0_0_21399491_23499.cpp:8:14: error: 'const double nan' redeclared as different kind of symbol
 const double nan=1e-6;
              ^
In file included from GCC4.9.2/x86_64-w64-mingw32/include/c++/cmath:44:0,
                 from GCC4.9.2/x86_64-w64-mingw32/include/c++/random:38,
                 from GCC4.9.2/x86_64-w64-mingw32/include/c++/bits/stl_algo.h:66,
                 from GCC4.9.2/x86_64-w64-mingw32/include/c++/algorithm:62,
                 from 0_0_21399491_23499.cpp:4:
GCC4.9.2/x86_64-w64-mingw32/include/math.h:931:25: note: previous declaration 'double nan(const char*)'
   extern double __cdecl nan(const char *tagp);
                         ^
0_0_21399491_23499.cpp: In function 'double getans(double, int)':
0_0_21399491_23499.cpp:29:32: error: invalid operands of types 'double' and 'double(const char*)' to binary 'operator>'
             while(num[i]<=n&&c>nan)
                                ^