Swapping variables

[jaberwacky]

My question is about a particular method of swapping variables.

$x -= $y
$y += $x
$x = $y - $x

My question involves the last line.

$x is subtracted from $y and then the result is stored back into $x.

In order to store the result back into $x then wouldn't there need to be a variable to store the result temporarily?

Otherwise the result would be lost right.?

[JohnOne]

As far as I se, those variables are swapped.

[squid808]

Nope, I often use a variable in the same line as I redefine it to no ill effect. For instance, when I'm working with names I can do something like the following:

$name="squid808"
$name=stringtrimright($name,stringlen($name)-2)
msgbox(0,"Hi","The first two letters of my SN are " & $name)

You don't have to worry about having a temporary or swap variable to hold on to things.

[jaberwacky]

I'm thinking behind the scenes here like what would the compiler do? ... wwcd ...

[omikron48]

Those variables are memory locations. What happens is, when you perform a calculation, the instruction for the operation is loaded into the CPU with all its flags and registers. After the calculation is performed, the result is then stored into whatever memory location is referenced by the variable.

So in essence, the CPU will be temporarily holding on to the result so there's nothing stopping you from storing the result in the same memory location as one of the parameters used for the calculation.

Edited July 21, 2010 by omikron48

[ShawnW]

I'm thinking behind the scenes here like what would the compiler do? ... wwcd ...

There is no compiler. This is an interpreted language. The .exe is an illusion just containing the source and interpreter with instructions on what to do.

[jaberwacky]

Those variables are memory locations. What happens is, when you perform a calculation, the instruction for the operation is loaded into the CPU with all its flags and registers. After the calculation is performed, the result is then stored into whatever memory location is referenced by the variable.

So in essence, the CPU will be temporarily holding on to the result so there's nothing stopping you from storing the result in the same memory location as one of the parameters used for the calculation.

Ok, so it would take two or three registers?

There is no compiler. This is an interpreted language. The .exe is an illusion just containing the source and interpreter with instructions on what to do.

I never knew that! thanks

[Richard Robertson]

Another way to switch (works on integers, which includes characters and pointers).

A XOR EQUALS B

B XOR EQUALS A

A XOR EQUALS B

The values are now swapped.