View Compilation Error

0_0_35447737_7863.cpp:8:14: error: 'const double exp' redeclared as different kind of symbol
 const double exp=1e-8;
              ^
In file included from GCC4.9.2/x86_64-w64-mingw32/include/c++/cmath:44:0,
                 from 0_0_35447737_7863.cpp:5:
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_35447737_7863.cpp: In function 'bool spfa()':
0_0_35447737_7863.cpp:47:54: error: 'esp' was not declared in this scope
             if(e[i].va>0&&dis[e[i].to]>dis[u]+e[i].c+esp)
                                                      ^