Undefined behavior (language)

Undefined behavior is a language where

Known UB programs

Hello, World!

   STATEMENT WHOSE BEHAVIOR IS ACTUALLY DEFINED
   IN AN UNDEFINED WAY, SET THE REGISTER 1 TO THE UNDEFINED VALUE // sets reg 1 to 0 or sometimes 255
   SET REGISTER 1 TO THY ZERO
   ASSIGN TO REGISTER_MULTI 1 TO LENGTH_OF STRING Hello, World! /STRING /LENGTH_OF /REGISTER_MULTI THE VALUE STRING Hello, World! /STRING // the only way that works with most compilers
   PRINT REGISTER_MULTI 1 TO LENGTH_OF STRING Hello, World! /STRING /LENGTH_OF /REGISTER_MULTI

Implementations

By definition,