C++ style: How to write clear code

Remove gratuitous complexity. This function adores gratuitous local variables! It contains three examples. First, the variable iDst is initialized to last-first and then used only once; why not just write last-first where it's used and get rid of clutter? Second, the vector iterator vit is created where a subscript was already available and could have been used just as well, and the code would have been clearer. Third, the local variable it gets initialized to the value of a function parameter, after which the function parameter is never used; my personal preference in that case is just to use the function parameter (even if you change its value—that's okay!) instead of introducing another name.