To redirect all your directories to c.php file, use these directives:
RewriteCond %{REQUEST_URI} -dRewriteRule (.+) c.php [R,QSA]
To redirect all the unexisting files to c.php then use:
RewriteCond %{REQUEST_URI} !-fRewriteCond %{REQUEST_URI} !-dRewriteRule (.*) c.php [R,QSA]