View Compilation Error

0_0_31008767_8481.cpp: In function 'int main()':
0_0_31008767_8481.cpp:3:31: error: 'scanf' was not declared in this scope
 #define read(a) scanf("%d", &a)
                               ^
0_0_31008767_8481.cpp:17:11: note: in expansion of macro 'read'
     while(read(n) && n != 0)
           ^
0_0_31008767_8481.cpp:22:30: error: 'sort' was not declared in this scope
         sort(a + 1, a + n + 1);
                              ^
0_0_31008767_8481.cpp:28:81: error: 'sqrt' was not declared in this scope
                 double s = sqrt(p * (p - a[i]) * (p - a[i - 1]) * (p - a[i - 2]));
                                                                                 ^
0_0_31008767_8481.cpp:35:29: error: 'printf' was not declared in this scope
         printf("%.2f\n", ans);
                             ^