The guard is a proposition, which must be true before the statement is executed. At the start of that statement's execution, one may assume the guard to be true. Also, if the guard is false, the statement will not be executed. The use of guarded commands makes it easier to prove the program meets the specification.

What are guarded commands in programming language?

The term guarded command, as defined by Dijkstra (1975), is synonymous with a conditionally executed statement. More precisely, a guarded command is the combination of a condition (boolean expression) B and the (possibly compound) statement S whose execution is controlled by B.

What is a guarded if statement?

Guarded if-statements: Together the branches must be logically complete, that is, under all circumstances at least one branch condition must hold. If more than one condition holds, one of these branches is chosen, indeterminately (in the implementation: randomly)