View Compilation Error

0_0_13955704_30000.cpp:5:1: error: 'usingnamespace' does not name a type
 usingnamespace std;
 ^
0_0_13955704_30000.cpp: In function 'int main()':
0_0_13955704_30000.cpp:32:19: error: 'sort' was not declared in this scope
     sort(a,a+n,cmp);
                   ^
0_0_13955704_30000.cpp:32:19: note: suggested alternative:
In file included from GCC4.9.2/x86_64-w64-mingw32/include/c++/algorithm:62:0,
                 from 0_0_13955704_30000.cpp:4:
GCC4.9.2/x86_64-w64-mingw32/include/c++/bits/stl_algo.h:4705:5: note:   'std::sort'
     sort(_RandomAccessIterator __first, _RandomAccessIterator __last,
     ^
0_0_13955704_30000.cpp:54:5: error: 'return0' was not declared in this scope
     return0;
     ^