how to make info channel ?

See implementation of function channel_message_send. There are only message_type_talk and message_type_emote types are handled to send to all users in channel. So you can use it like in _handle_me_command function. All users will see who use command /x:

static int _handle_infochannel_command(t_connection * c, char const * text)
{
  t_channel const * channel;

  if (!(channel = conn_get_channel(c)))
    {
      message_send_text(c,message_type_error,c,"You are not in a channel.");
      return 0;
    }

snprintf(msgtemp, sizeof(msgtemp), "Info Channel from %.64s: %.128s",conn_get_username(c),&text[i]);
channel_message_send(channel,message_type_emote,c,msgtemp);

return 0;
}

Or you can iterate all users connections, check current channel of each and do something you want:

LIST_TRAVERSE_CONST(connlist(),curr)
    {
    c = (t_connection*)elem_get_data(curr);
    // your code
    }

Read the error message - 'i' is undeclared identifier.
I don't know why did you use &text{i} (mindless copy-paste?), look at the function _handle_me_command in command.cpp and do the same.