View Compilation Error

0_0_21130949_2847.cpp:6:14: error: 'const double exp' redeclared as different kind of symbol
 const double exp = 1e-9;
              ^
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_21130949_2847.cpp:2:
GCC4.9.2/x86_64-w64-mingw32/include/math.h:148:18: note: previous declaration 'double exp(double)'
   double __cdecl exp(double _X);
                  ^
0_0_21130949_2847.cpp: In function 'int main()':
0_0_21130949_2847.cpp:33:26: error: invalid operands of types 'double' and '<unresolved overloaded function type>' to binary 'operator<'
   if (sum-(__int64)sum < exp){
                          ^
0_0_21130949_2847.cpp:38:27: error: invalid operands of types 'double' and '<unresolved overloaded function type>' to binary 'operator<'
    if (sum-(__int64)sum < exp){
                           ^