Using insert_data and to_array functions from my Binary Search Tree project as my mystery sort on my Sorting Algorithms project.

Sorting with a BST

// This mystery_sort is going to use my insert_data and to_array function from BST project! 

void mystery_sort(vector<int> &data) 
{

	bt_node* top = init_node(data[0]); 
	
  // Looping through the data and adding it to my BST.
  // ...Using my insert_data function which calls my insert function.
	for (unsigned int i = 1; i < data.size(); i++)
		insert_data(&top, data[i]); 
	
  // Need to set the size of an array before I can use it. 
	int arr [size(top)]; 
  
  // Now adding my items in the tree to an array.  
	to_array(top, arr);
	
	// Now getting the sorted data out of the array and putting it back in the data vector! 
	for (int i = 0; i < size(top); i++)
		data[i] = arr[i]; 

}

Is it critical to use post-increment (i++)? If not, it's better to be changed to ++i, I suppose.