View Compilation Error

0_0_37849486_29390.cpp: In function 'int main()':
0_0_37849486_29390.cpp:19:18: error: no match for 'operator[]' (operand types are 'std::set<int>' and 'int')
    scanf("%d", &a[i]);
                  ^
0_0_37849486_29390.cpp:20:14: error: no match for 'operator[]' (operand types are 'std::set<int>' and 'int')
    a.insert(a[i]);
              ^
0_0_37849486_29390.cpp:26:18: error: no match for 'operator[]' (operand types are 'std::set<int>' and 'int')
    scanf("%d", &b[i]);
                  ^
0_0_37849486_29390.cpp:27:14: error: no match for 'operator[]' (operand types are 'std::set<int>' and 'int')
    b.insert(b[i]);
              ^