Passing a vector by reference and changing its values in a range-based for loop?

Question

I'm trying to change the values of a vector by doing something similar to the following function:

vector<int> Question2_Part3(vector<int> &v){

    for(auto elem : v){
        elem *= 2;
        cout << elem << " ";
    }
    cout << "\n" << endl;

    return v;
}

Is this possible? I know that in my for loop, it is the value of elem that is changing. Can I have the same output while also changing the values in v and still use a range-based for loop?

Answer 1

Yes it is possible but use a reference

for (auto &elem : v) {
    elem *= 2;
    cout << elem << " ";
}

This is also more efficient as it avoids copying each vector element to a variable. Actually if you didn't want to change the elements you should do

for (const auto &elem : v) {
    cout << elem << " ";
}

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