View Compilation Error

0_0_35971559_23822.cpp: In member function 'void polygon::norm()':
0_0_35971559_23822.cpp:84:23: error: 'sort' was not declared in this scope
   sort(p, p+n, cmp(mi));
                       ^
0_0_35971559_23822.cpp: In member function 'void polygon::getconvex(polygon&)':
0_0_35971559_23822.cpp:88:14: error: 'sort' was not declared in this scope
   sort(p, p+n);
              ^