ItemUpdated Event Receiver how to change element from one list to secound list

Question

I have got two lists. I must do synchronize this list, but one have got only 3 columns, and secound list have got 3 columns too, but have got more columns with hidden value. I done synchronizing adding, but I must do ItemUpdated to. Because if i change a value in 3 columns in first list it should change in secaund list. Adding was done by this code Event Receiver:

   public override void ItemAdded(SPItemEventProperties properties)
    {
        this.EventFiringEnabled = false;
        base.ItemAdded(properties);
        if (properties.List.Title == "Jawna")
        {
            using (SPSite site = new SPSite(properties.WebUrl))
            {
                using (SPWeb web = site.OpenWeb())
                {
                    SPList lstOtherList = properties.Web.Lists["Niejawna"];
                    SPListItem item = lstOtherList.Items.Add();
                    web.AllowUnsafeUpdates = true;
                    item["Title"] = properties.AfterProperties["Title"];
                    item["B"] = properties.AfterProperties["B"];
                    item["Status"] = properties.AfterProperties["Status"];
                    item.Update();

                }
            }
        }
        if (properties.List.Title == "Niejawna")
        {
            using (SPSite site = new SPSite(properties.WebUrl))
            {
                using (SPWeb web = site.OpenWeb())
                {
                    SPList lstOtherList = properties.Web.Lists["Jawna"];
                    SPListItem item = lstOtherList.Items.Add();
                    web.AllowUnsafeUpdates = true;
                    item["Title"] = properties.AfterProperties["Title"];
                    item["B"] = properties.AfterProperties["B"];
                    item["Status"] = properties.AfterProperties["Status"];
                    item.Update();

                }
            }
        }
        this.EventFiringEnabled = true;
    }

How to done the same with items update ? I think it should be the Caml Query, or linq query. But how ? Please help me. To change only this element wchich have got 3 Colums the same as in first List.

Updated Question:

I write the code:

    public override void ItemUpdated(SPItemEventProperties properties)
    {
        this.EventFiringEnabled = false;
        base.ItemUpdated(properties);
        if (properties.List.Title == "Jawna")
        {
            using (SPSite site = new SPSite(properties.WebUrl))
            {
                using (SPWeb web = site.OpenWeb())
                {
                    SPList lstOtherList = properties.Web.Lists["Niejawna"];
                    string fieldA = properties.ListItem["Title"].ToString();
                    string fieldB = properties.ListItem["B"].ToString();
                    string fieldStatus = properties.ListItem["Status"].ToString();

                    SPQuery query = new SPQuery();
                    query.Query = "<Where><Eq><FieldRef Name='Field A'/><Value Type='Text'>" + fieldA + "</Value></Eq></Where>";

                    SPListItemCollection items = lstOtherList.GetItems(query);
                    SPListItem item = items[0];

                    item["Title"] = properties.ListItem["Title"];
                    item.Update();
                }
            }
        }
        this.EventFiringEnabled = true;
    }

And I getting now this error:

One or more field types are not installed properly. Go to the list settings page to delete these fields.

Answer 1

Firstly there's no value for properties.AfterProperties in the ItemAdded event receiver. You can see in what receivers After- and Before- properties are available here.

To get a field's value use properties.ListItem['FieldName'].

To synchronize appropriate items in both lists you should have some unique field to search items. If you have Title field as a unique one you can search item using this CAML query:

var query = new SPQuery();
query.Query = "<Where><Eq><FieldRef Name='Title' /><Value Type='Text'>Searched Title</Value></Eq></Where>";
var items = list.GetItems(query);