View Compilation Error

0_0_35749981_28165.cpp: In function 'int main()':
0_0_35749981_28165.cpp:12:3: error: 's' was not declared in this scope
   s.clear();
   ^
0_0_35749981_28165.cpp:14:44: error: 'a' was not declared in this scope
   for(int i = 0; i < n; i++) scanf("%lld",&a[i]);
                                            ^
0_0_35749981_28165.cpp:19:14: error: 'a' was not declared in this scope
     s.insert(a[i]+a[j]); 
              ^