Redirect checkout pages to https and back to http

My site makes use of a dedicated SSL certificate.

Read through all the solutions given in this forum about redirect to https and back to http.
I am not sure what to use in my site.

1__Do I have to use both the following scripts in the cartpage :

on line 1:

<?php*if((!(isset($_SERVER['HTTPS'])))*||*($_SERVER['HTTPS']*==*"")*||*($_SERVER['HTTPS']*==*"off"))header("Location:*https://"*.*$_SERVER['HTTP_HOST']*.*$_SERVER['PHP_SELF']);*?>

and change the redirect
from
$Redirect_redirStr="checkout.php";
to
$Redirect_redirStr="https://www.mydomain.com/checkout.php";

2__ Does this redirect influence the : $WAFV_Redirect = "checkout.php"; on my confirm page ?

3__Do all links/menulinks to http pages from these checkout pages need the following code on line 1 to go back to http ?

<?php*if((!(isset($_SERVER['HTTPS'])))*||*($_SERVER['HTTPS']*==*"")*||*($_SERVER['HTTPS']*==*"off"))header("Location:*http://"*.*$_SERVER['HTTP_HOST']*.*$_SERVER['PHP_SELF']);*?>

or
do I have to use the link http://www.mydomain.com/somepage.php for all of them.

Would appreciate some help !

on any page that should be served using the HTTPS address, add this code at line 1:

<?php if((!(isset($_SERVER['HTTPS']))) || ($_SERVER['HTTPS'] == "") || ($_SERVER['HTTPS'] == "off"))header("Location: https://www.<your domain here>" . $_SERVER['PHP_SELF']); ?>

on any page that should not be served through the HTTPS address, add this code at line 1:

<?php

if (isset($_SERVER['HTTPS']) && strtolower($_SERVER['HTTPS']) == 'on') header("Location: http://".$_SERVER['HTTP_HOST'].$_SERVER['PHP_SELF']); ?>

the code snippet will cause any page accessed using the HTTP address to redirect to the HTTPS address, the second will reverse it.

aside from the checkout redircet:
$Redirect_redirStr="https://www.mydomain.com/checkout.php";


no other changes will be necessary.

Thank you Jason for a quick and very clear answer.

Appreciate your help !!!