C# Array Map/Collect

a = a.Select( s => s + "!" ).ToArray();

I prefer using ConvertAll since it's quicker and I believe more intuitive.

var a = a.ConvertAll(x => x + "!").ToArray();

Since I prefer the naming, I personally use my own Enumerable Map Extension methods which is available to all IEnumerable<T> Types, guards against null and follows the standing naming in other languages for functinoal projection.

var to = a.Map(x => x + "!");