You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: quad4_quad8.m
    path of file: ./repos/GIBBON/lib
    
    the code of the file until where you have to start completion: function [varargout]=quad4_quad8(varargin)


    
function [varargout]=quad4_quad8(varargin)

% function [QUAD8,V8,VX8C]=quad4_quad8(QUAD4,V4,VXC)
%
% This function converts 4 node (e.g. linear) quadrilaterial elements into
% 8 node (e.g. quadratic) quadrilateral elements compatible with FEBio.
%
% Kevin Mattheus Moerman
% gibbon.toolbox@gmail.com
%
% 2018/10/19 Created based on tri3_tri6
%----------------------------------------------------------------------
%%

switch nargin
    case 2
        QUAD4=varargin{1};
        V4=varargin{2};
        VXC={};
    case 3
        QUAD4=varargin{1};
        V4=varargin{2};
        VXC=varargin{3};
end