c# have an index in string.join? code example

Example 1: c# list join

List<string> names = new List<string>() { "John", "Anna", "Monica" };
var result = String.Join(", ", names.ToArray());

Example 2: c# array.join

String Array...
AB
BC
CD
DE
EF
FG
GH
IJ
Result (after joining) = AB*BC*CD*DE*EF*FG*GH*IJ