Passing variables to Plugins

[datarecall]

Hello,

I am making an ad server plugin however I am trying to figure out a way to pass variables into the functions, I have only done a couple plugins and they have always used placement variables like $put_plugin_content_here but is there a way to call a plugin function,
$my_plugin_name($var_to_pass)
ie: plugin_name(4)

Thanks for the help