Code with undefined behavior in C#

Question

In C++ there are a lot of ways that you can write code that compiles, but yields undefined behavior (Wikipedia). Is there something similar in C#? Can we write code in C# th

Answer 1

According to the ECMA-334 document (p. 473):

A program that does not contain any occurrences of the unsafe modifier cannot exhibit any undefined behavior.

That promotes 'implementation-defined' to the worst case, see Eric Lippert's answer.