Standard containers encapsulation and range-based for loops

I'm designing a class which has two standard vectors as members. I would like to be able to use range-based for loops on the vector elements and I came up with this solution

#include <iostream>
#include <vector>

using namespace std;

class MyClass {
public:
  void addValue1(int val){data1_.push_back(val);}
  void addValue2(int val){data2_.push_back(val);}
  vector<int> const & data1() const {return data1_;}
  vector<int> const & data2() const {return data2_;}
  // ...
private:
  vector<int> data1_;
  vector<int> data2_;
  // ...
};

void print1(MyClass const & mc) {
  for (auto val : mc.data1()){
    cout << val << endl;
  }
}

void print2(MyClass const & mc) {
  for (auto val : mc.data2()){
    cout << val << endl;
  }
}

int main(){
  MyClass mc;
  mc.addValue1(1);
  mc.addValue1(2);
  mc.addValue1(3);
  print1(mc);
}

Clearly, the alternative of defining begin() and end() functions doesn't make sense since I have two distinct vectors.

I would like to ask the following questions:

• A shortcoming of the proposed solution is that the contents of the two vectors cannot be changed (due to the const qualifier). In the case I need to modify the vector elements how can I modify the code?

• Considering data encapsulation, do you think it is bad practice to return a (const) reference to the two vectors?