Question

I want to plus 3 to all list<int> member without using for loop or foreach loop ? Can I do this in one line ?How?

Answer 1

Something somewhere is going to have to loop. You don’t have to loop in your code, but something’s going to have to.

I can’t think of anything offhand which will modify all the elements in a list, but using LINQ you could create a new List<int> easily:

var plusThree = originalList.Select(x => x + 3).ToList();

or pre-LINQ (and slightly more efficient, but also more List<T>-specific):

var plusThree = originalList.ConvertAll(x => x + 3);

But both of these will be looping behind the scenes.

You could potentially create a projecting IList<T> implementation which lazily applied a projection (or possibly a bijection if you wanted to be really fancy)… but that would be significant amounts of work.