Question

Can anyone give me some examples errors that may occur in execution time, compilation undetectable using the foreach structure in C#?

Answer 1

The most common it would be modifying your collection

foreach (var item in collection)
{
  //the following statements would generate an error.
  collection.Add(new Item());
  collection.Remove(item);
}

you cannot modify your collection structure while enumerating through it.
You can modify the items inside the collection, not the collection.

Another error you might have is if the collection is null. It is a good idea to check if a collection is null before enumerating.

I think getting any other error is because the logic inside the statement is wrong, not because you are in a foreach loop.