View Compilation Error

0_0_20151119_2035.cpp: In function 'int main()':
0_0_20151119_2035.cpp:14:17: error: 'sort' was not declared in this scope
   sort(a+1,a+n+1);
                 ^
0_0_20151119_2035.cpp:18:30: error: 'next_permutation' was not declared in this scope
    next_permutation(a+1,a+n+1);
                              ^