PBasic's MIN and MAX operator precedence.

Martin_H

In many programming languages MIN and MAX are functions, so the order of operations is clear. But in PBasic they are binary operators, so I assume they have operator precedence. Look at this code for example:

byte a
byte b
byte c

a = 1
b = 2
c = 3

// All MAX is a slam dunk, it should display 3
DEBUG a MAX b MAX c 

// If this is evaluated left to right it should output 2.
DEBUG a MAX b MIN c

// But what happens when you mix in other mathematical operators?
DEBUG a MAX b + 1 MIN c

// What about multiply which takes precedence over other operators?
DEBUG a MAX b * 2 MIN c

Basically, my question is how do MIN and MAX fit into the order of operators precedence?

Phil Pilgrim (PhiPi)

There is no operator precedence in PBASIC: evaluation is strictly left-to-right unless modified by parentheses.

-Phil

Martin_H

Thanks Phil, that explains why I couldn't seem to find anything about it in the manual. It also explains my odd bug.

I can't believe I've been using PBasic for six years and hadn't noticed that by now. I always assumed it was like other languages which attempt to reproduce the mathematical precedence. Since I tend to avoid compound expressions and heavy math in PBasic I've gotten lucky up to now.

Tracy Allen

You'd think slam dunk:

[FONT=courier new][SIZE=1]a = 1
b = 2
c = 3

// All MAX is a slam dunk, it should display 3
DEBUG a MAX b MAX c 
[/SIZE][/FONT]

but the answer is 1, not 3. That is because the MAX operator sets a ceiling.

You can think of it as,
y = x MAX 3
and that is either x or 3, whichever is less. So 3 is the ceiling.

Okay, but it is equally true that
y = 3 MAX x
is either x or 3, whichever is less. The same as above. The operator is said to be commutative. So with your set of values a=1, b=2 and c=3, the MAX operator ends up picking the minimum value. Tricky huh?

Martin_H

Tracy Allen wrote: »

So with your set of values a=1, b=2 and c=3, the MAX operator ends up picking the minimum value. Tricky huh?

OK I was completely confused. I thought these were like the C functions of the same name, but it sounds like they are reversed. In C max (1, 3) returns 3, while min(1, 3) returns 1. I have a minor rewrite to do.

Tracy Allen

Right, quite the opposite of what you would expect from the mathematical perspective of finding the max or min of a pair or set of numbers. It is more helpful to think of it in the context of process control, where you need to hold a variable to values between a max and a min.

Phil Pilgrim (PhiPi)

I like to think of MAX as "but no more than" and MIN as "but no less than." Same goes for Spin, but at least its operators are more intuitive.

-Phil