how to use power operator, like x^y? 2

[RajVerma]

hi all,

I have a strange observation when I was using the symbol ^ thinking that it is like power. but I'm getting the following results that I cudn't understand.

[expr 2^1] = 3
[expr 2^2] = 0
[expr 2^3] = 1
[expr 2^4] = 6
[expr 2^5] = 7
[expr 2^6] = 4
[expr 2^7] = 5
[expr 2^8] = 10
[expr 2^9] = 11
[expr 2^10] = 8
[expr 2^11] = 9

and so on. So my question is what exavtly does this ^ operator do? and how to use power operator?

thanx a lot,
Raj.

 

[ddrillich]

http://www.tec.ufl.edu/~flooxs/FLOOXS Manual/TclTk/tcl8.0/expr.n.html

says:
^ Bit-wise exclusive OR. Valid for integer operands only.

So:

2^1: 00000010 exclusive OR 00000001 = 00000011 = 3
2^2: 00000010 exclusive OR 00000010 = 00000000 = 0
2^3: 00000010 exclusive OR 00000011 = 00000001 = 1


I found the proc power at

http://people.uncw.edu/adharg/courses/csc342/TclTk/tcltk.html:

proc power {base p} {
set result 1
while {$p>0} {
set result [expr $result*$base]
set p [expr $p-1]
}
return $result
}

Regards,
Dan

 

[AviaTraining]

There's a much easier way. For over 10 years (since Tcl 7.0), expressions have supported the pow() function. pow() accepts 2 floating-point arguments, like [tt]pow($x,$y)[/tt], which would raise x to the y power:

[tt]% set x 2
2
% expr { pow($x, 2) }
4.0
% expr { pow($x, 10) }
1024.0
% expr { pow($x, 5.75) }
53.8173705762[/tt]

As a side note, it's recommended practice -- for performance and other reasons -- to enclose the arguments to expr inside of curly braces {}. See the Tcl'ers Wiki page "expr,"

http://wiki.tcl.tk/583,

for more information and other helpful tips on Tcl expressions. Also check out the expr command reference,

http://purl.org/tcl/home/man/tcl8.4/TclCmd/expr.htm,

for a complete list of supported functions and operations.

- Ken Jones, President, ken@avia-training.com
Avia Training and Consulting,

http://www.avia-training.com

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