Idiom for doing something twice in C++

Question

Is there a common idiom for doing something twice, as in the following situation?

    for ( int i = 0; i < num_pairs; i++ ) {
        cards.push_back( Card(i) );
        cards.push_back( Card(i) );
    }

I have a feeling that there's a clearer way than introducing a new loop variable counting from 0 to 1, especially since it isn't used except for counting.

    for ( int i = 0; i < num_pairs; i++ )
        for ( int j = 0; j < 2; j++ )
            cards.push_back( Card(i) );

(Card is just some class I made up and not relevant to the question.)

Answer 1

You probably want to use the fill_n function in <algorithm>

for ( int i = 0; i < num_pairs; i++ )
    std::fill_n(std::back_inserter(cards), 2, Card(i));

Answer 2

Personally I would just leave it how it is. It looks clean, it's easy to understand, and it's quite readable. Just leave a comment mentioning why you do it twice (but you would do that no matter what).