View Compilation Error

0_0_21424374_29151.cpp: In function 'int main()':
0_0_21424374_29151.cpp:34:27: error: 'sort' was not declared in this scope
         sort(a+1,a+1+n,cmp);  
                           ^
0_0_21424374_29151.cpp:34:27: note: suggested alternative:
In file included from GCC4.9.2/x86_64-w64-mingw32/include/c++/algorithm:62:0,
                 from 0_0_21424374_29151.cpp:3:
GCC4.9.2/x86_64-w64-mingw32/include/c++/bits/stl_algo.h:4705:5: note:   'std::sort'
     sort(_RandomAccessIterator __first, _RandomAccessIterator __last,
     ^