Generating sequential indices using LINQ

Calculating index using index++.

int index = 0;
words = new ObservableCollection<LookupItem>(
    // trick number 1: converting string into char[]
    from word in "Hello world from LINQ".Split(" ".ToCharArray())
    select new LookupItem { Caption = word, Index = index++ }));

The same using built-in LINQ functionality.

words = new ObservableCollection<LookupItem>(
    "Hello world from LINQ".Split(" ".ToCharArray()).
    // trick number 2: generating sequential numbers using LINQ
    Select((word, index) => new LookupItem { Caption = word, Index = index }));

Other useful LINQ functions having second form with index are TakeWhile, SkipWhile and Where.

words = new ObservableCollection<LookupItem>(
    "Hello world from LINQ".Split(" ".ToCharArray()).
    Where((word, index) => index < 100).
    Select((word, index) => new LookupItem { Caption = word, Index = index }));