.htaccess rewrite - filename.html to /?c=filename - apache

Question

I need it to work with all html URLs (except index), I tried using .htaccess with no luck.
For example... change this link from: http://www.example.com/signup.html to http://www.example.com/?c=signup.
Also if I enter directly to http://www.example.com/?c=signup, it must mirror http://www.example.com/signup.html.
EDIT
I found the way to do that, except for the case that I enter directly to the .html file, in that case, it does not rewrite.
Options +FollowSymLinks -MultiViews
RewriteEngine On
RewriteCond %{QUERY_STRING} ^c=([^&]+) [NC]
RewriteRule ^/?$ %1.html [NC,L,QSA]

Answer 1

RewriteRule ^/?$ %1.html [NC,L,QSA]
To redirect (presumably you meant "redirect", not "rewrite") from signup.html to /?c=signup then you can do something like the following before your existing rewrite:
RewriteCond %{ENV:REDIRECT_STATUS} ^$
RewriteRule ([^.]+)\.html$ /?c=$1 [R,L]
The condition that checks against the REDIRECT_STATUS environment variable prevents a redirect loop when your existing directive rewrites to the .html file.
Note that this is a temporary (302) redirect. Change the R to R=301 if this is intended to be permanent, but only once you have confirmed it's working OK.
Your existing directives could be tidied, in summary:
Options +FollowSymLinks -MultiViews
RewriteEngine On
# Redirect from signup.html to /?c=signup
RewriteCond %{ENV:REDIRECT_STATUS} ^$
RewriteRule ([^.]+)\.html$ /?c=$1 [R,L]
# Rewrite from /?c=signup to signup.html
RewriteCond %{QUERY_STRING} ^c=([^&]+)
RewriteRule ^/?$ %1.html [QSD,L]
Presumably, you want to discard the c= query string from the rewritten substitution?