Rexx Programming/How to Rexx/boolean

Boolean values are logical truth values that are considered either true or false. Rexx uses 1 to mean "true" and 0 to mean "false". Some programming languages have many different kinds of values that could be treated as Boolean, depending on the context. The Rexx programming language itself only recognizes 0 and 1 for this purpose. /* Some Boolean variables */ raining = 1 freezing = 1 snowing = 0 hailing = 0 /* Boolean values affect control structures... */ /* The computer will say we might need an umbrella. */ select when raining then say "You might need an umbrella." when snowing then say "Let's build a snowman!" when hailing then say "Ouch! There's hail." otherwise say "There might not be any precipitation." end /* The computer will tell us to watch out for ice. */ if freezing then say "Watch out for ice!" else say "At least it's not freezing outside." /* This loop will never start because it isn't snowing. */ do while snowing say "It'll just keep snowing forever!" end Logical Operators Operators exist to combine Boolean values into new Boolean values. The ampersand (&) means "and", the pipe symbol (|) means "or" and the backslash (\) means "not". if raining | snowing then say "It's either raining or snowing--maybe both." if raining & freezing then say "Expect freezing rain." if \ snowing then say "No snow today." if \ (raining | snowing) then say "It's neither raining nor snowing." Relational Operators Some other operations combine other kinds of values to make true or false statements. They will always result in 0 or 1. You can read about them in the comparative operators section. The remainder when an integer is divided by 2 will technically result in a Boolean value, but other kinds of remainders will not. say 2 < 3 /* says 1 */ say "happy" = "sad" /* says 0 */ /* We can use Booleans to validate input: */ do until positive & even say "Enter a positive even number:" pull number positive = number > 0 odd = number // 2 even = \ odd end