Function problem_21

examples/99_problems.cpp:175–178

P21 (*) Insert an element at a given position into a list.

// P21 (*) Insert an element at a given position into a list.
void problem_21()
{
    print_result(insert_at_idx(3, -1, xs));
}

// P22 (*) Create a list containing all integers within a given range.
void problem_22()