Q:

String types not allowed (at 'id' with value ' @id/bAdd')

I am getting an error saying 
String types not allowed (at 'id' with value ' @id/bAdd')

I've cleaned the project.
Everything was working earlier, I don't what happened, causing this error. 
 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >

<TextView
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:layout_centerHorizontal="true"
    android:layout_centerVertical="true"
    android:text="Your total is 0"
    android:textSize="45dp"
    android:layout_gravity="center"
    android:gravity="center"
    android:id="@+id/tvDisplay"
    tools:context=".StartingPoint" />

 <Button 
    android:layout_width="250dp"
    android:layout_height="wrap_content"
    android:text="Subtract One"
    android:layout_gravity="center"
    android:textSize="20dp"
    android:id="+@id/bSub"
    />

<Button 
    android:layout_width="250dp"
    android:layout_height="wrap_content"
    android:text="Add One"
    android:layout_gravity="center"
    android:textSize="20dp"
    android:id="+@id/bAdd"

    />

A:

You can give your id as @+id/bAdd
instead of +@id/bAdd
Also edit in
android:id="@+id/bSub"
            ^^

instead of
android:id="+@id/bSub"
            ^^

A:

+ Symbol must be after @ Symbol.
android:id="+@id/bAdd" to  android:id="@+id/bAdd"

 and also change

android:id="+@id/bSub" to android:id="@+id/bSub"

OR
you can declare is it 
android:id="@id/bSub"
but you have to declare bSub value in ids.xml file located in values folder.
Example
<resources>
  <item type="id" name="bSub" />

