Basic AddOne function that adds one to each item in an IEnumerable<int> without using yield of foreach.

gistfile1.txt

// Write an AddOne method that doesn't use yield or foreach
static IEnumerable<int> AddOne(IEnumerable<int> items)
{
	var returnEnumer = Enumerable.Empty<int>();
	var enumerator = items.GetEnumerator();

	while(enumerator.MoveNext())
	{
		returnEnumer = returnEnumer.Concat(Enumerable.Repeat(enumerator.Current + 1, 1));
	}

	return returnEnumer;
}
	
void Main()
{
	var enumer = Enumerable.Repeat(1,1);
	enumer = AddOne(enumer);
	enumer.Dump();
}