While what's true?

Ruby
#1

Ex 35 … we’re in the game with a grouchy bear and the evil Cthulhu …

The definition of the bear_room function includes the following while loop, spanning lines 30 to 46 …

while true
	print "> "
	choice = $stdin.gets.chomp

	if choice == "take honey"
		dead("The bear looks at you then slaps your face off.")
	elsif choice == "taunt bear" && !bear_moved
		puts "The bear has moved from the door. You can go through it now."
		bear_moved = true
	elsif choice =="taunt bear" && bear_moved
		dead("The bear gets pissed off and chews your leg off.")
	elsif choice == "open door" && bear_moved
		gold_room
	else
		puts "I got no idea what that means."
	end
end

So the while loop begins …

while true

My question is … while what is true?? In the Common Student Questions for Ex 35, someone has asked why the code says “while true”? The response is that “while true” makes an infinite loop.

I thought we were supposed to avoid infinite loops, so this is even more puzzling. But - are we using an infinite loop here because we always want to go through this while loop when we’re in the bear_room?

I’d appreciate a little more explanation about “while true” … :slight_smile:

#2

Anything you put after while or if eventually boils down to true or false. That’s how boolean logic works. When you write a test like

while x < 3

then the programming language checks whether the precdiate x < 3 is true or false.
But single values also have a truth value, so if x is some integer, in

while x

the test evaluates to false if x is 0, otherwise it’ll be true. Generally speaking, most things that are not empty or zero are considered true in the context of boolean operations.

Combined with the fact that you can write ‘literal’ tests that don’t depend on a changing variable this allows you to write ‘infinite loops’. You usually do

while true

but you could also write

while 1

or

while "this is a tru-ish string"

to do the same thing: These ‘tests’ always evaluate to true so the loop never exits unless you tell it to explicitly in the body.

You generally don’t want a loop to never end, but infinite loops can be a useful construct if you make sure that there are explicit exit points. In your code there are two of them: the dead function and the gold_room function. The loop runs until it hits a condition that leads to either of those.

Does that help?

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#3

Got it!

That’s great - thanks, florian!

:grinning:

1 Like