View Compilation Error

0_0_37924231_31636.cpp:8:26: error: 'acos' was not declared in this scope
 const double PI=acos(-1.0);
                          ^
0_0_37924231_31636.cpp: In function 'int main()':
0_0_37924231_31636.cpp:24:2: error: 'ios' has not been declared
  ios::sync_with_stdio(0);
  ^
0_0_37924231_31636.cpp:25:2: error: 'cin' was not declared in this scope
  cin.tie(0);
  ^
0_0_37924231_31636.cpp:26:2: error: 'cout' was not declared in this scope
  cout.tie(0);
  ^
0_0_37924231_31636.cpp:37:17: error: 'sort' was not declared in this scope
   sort(a+1,a+n+1);
                 ^