Loop invariant

• Authors: David Gries
• Venue: Encyclopedia of Computer Science
• Year: 2003

Consider a loop while B do S, where B is a Boollean expression and S a statement. This form of loop appears in most modern high-level languages. Let P be some true-false statement about the variables of the programm in which the loop appears. P is a loop invariant if execution of the loop body S begun in any state in which P and B are true terminates with P true. For example, consider the loop