A common scenario is wanting to delete an item while iterating over a collection using foreach:

Unfortunately, this will give the dreaded InvalidOperationException:

Collection was modified; enumeration operation may not execute.

This is because modifying the state of a collection invalidates the enumerator that foreach uses behind the scenes to loop over the collection.

A common work-around is to convert the foreach to a for loop:

You'll notice that the for loop goes backwards from the end of the list (position: Count - 1) back to the start (position: 0), so that when an item is removed, our current index i is still a valid position in the list.

How do you do it?

Kirk

Source (such that it is) Program.txt