operator ^ for power

[GPI]

I was suprised, that purebasic miss one basic operator

Code: Select all

debug 2^5
debug 2*2*2*2*2
debug pow(2,5)

all should output 32. In case of 2^5 it shoud create a integer, because no float/double is evolved.

Code: Select all

  Priority Level |     Operators
  ---------------+---------------------
       8 (high)  |      ~, -
      7.5       |       ^
       7         |    <<, >>, %, !
       6         |       |, &
       5         |       *, /
       4         |       +, -
       3         | >, >=, <, <=, =, <>
       2         |       Not
       1 (low)   |  And, Or, XOr

[Little John]

If such an operater will be implemented in PB, then it should work mathematically correct!

Unfortunately, I've often seen in expression evaluators that something like
4^3^2 is evaluated from left to right, which is mathematically wrong:
(4^3)^2 = 64^2 = 4096

Correctly, multiple power operators without any brackets are evaluated from right to left:
4^3^2 = 4^(3^2) = 4^9 = 262144

^ is right associative, and there is no doubt about it.

[GPI]

thanks for the info
(I write a eval routine )

[Little John]

You are welcome!

(I write a eval routine )

Here is some related code by me.

[jwrjrjwrjr]

+1 on the request and on the proper implementation!

[GPI]

maybe important:
-9^2 is equal to -(9^2)

(thanks to little john)

[Little John]

GPI, you are welcome!

For the skeptics.
Wolfram Alpha: -9^2

[skywalk]

Same with Windows Calculator:
-9^2 = 0 - 9^2 = -81.

[GPI]

GPI, you are welcome!

For the skeptics.
Wolfram Alpha: -9^2

Good example
http://www.wolframalpha.com/input/?i=3%2B-2

In your code this is illegal

Code: Select all

Check("3+-2",     Eval::#Err_BadSyntax)

[Little John]

In your code this is illegal

Code: Select all

Check("3+-2",     Eval::#Err_BadSyntax)

How strict the syntax checking is, is another story.
My parser does deliberately rather strict syntax checking.

With Wolfram Alpha, even this works:
http://www.wolframalpha.com/input/?i=nine+to+the+power+of+two
http://www.wolframalpha.com/input/?i=nine+to+power+of+two
http://www.wolframalpha.com/input/?i=nine+to+power+two

However, I think this is a bit offtopic here in the "Feature Requests" section.

[Lord]

maybe important:
-9^2 is equal to -(9^2)

(thanks to little john)

I don't think so.
You have to differentiate between
a minus sign as a indicator for a negative number -> (-9)
example: http://www.wolframalpha.com/input/?i=(-9)^0.5
and
a minus sign as a calculation rule -> -(9)
example: http://www.wolframalpha.com/input/?i=-+(9^0.5)

You have to set correct parenthesis in order to get a correct result.

[Little John]

You have to set correct parenthesis in order to get a correct result.

No.
You can set parentheses, but in this case you don't necessarily have to do so.
You only have to set parentheses here, if you want to calculate (-9)^2.
As GPI wrote, -9^2 "automatically" means the same as -(9^2).
Just like e.g. 3 + 4 * 5 means the same as 3 + (4 * 5).
Those are well established math rules, regardless whether you believe it or not.

[Lord]

...regardless whether you believe it or not.

We are not in church here, arent we?

Same with Windows Calculator:
-9^2 = 0 - 9^2 = -81.

Just try these steps:
[-][9][=][x^y][0][,][5]
against
[-][9][x^y][0][,][5]
It shows that in the first example the calculator tried to get the root of a negative number (-9).
The second example interprets the minus sign as a calculation rule (subtract 9^0.5 from something, here from 0 as there is nothing before).

If we leave square roots and try to get a cubic root, both ways lead to valid results (for example -27 -> -3).
So dealing with odd roots there is no problem, but with even roots you have to make clear wether you want to subtract a result or get a root from negativ number.

[Little John]

...regardless whether you believe it or not.

We are not in church here, arent we?

No, we are not in church here. I'm glad that we seem to be in agreement about this.

[GPI]

@lord
I think, that -9^2 = (-9)^2 would make more sense, but it is -(9^2).

For example try to goolge for "-9^2".