php recursive variable won't change

Question

I have a function like:

myfunction($i,$condition = false, $level = 0) {
   do {
      if (... some conditions here)   { myfunction($i, true, ++$level) }
      else { do something here ... }
   while ( ...meet ending condition )
}

I don't understand why the $condition turn true when i call myfunction() recursively and come back to false when iterating in first level and $level won't turn to 0 after it exits a recursive mode.

$condition = false, false, true, false, false, true, true, true ...

$level = 0,0,1,1,1,2,2,2 ... it shoul also be like = 0,0,1,0,0,1,2,2,2,0 ... and so on ?

Thank you

P.S : It is the same with arrays ? I declared an array in the function set to null and when exits the recursive mode it's not null anymore :

myfunction($i,$condition = false, $level = 0, $array = null) {
       do {
    if($condition) { $array = null }    <--------- I HAVE TO ADD THIS LINE TO MAKE IT NULL WHY ?
          if (... some conditions here)   {$array = Array(someblabla); myfunction($i, true, ++$level, $array) }
          else { do something here ... }
       while ( ...meet ending condition )
    }

Thanks to all ... $level+1 did the trick as you said. But i don't know why and where is menitoned in the php`s references . — pufos
– pufos, Commented Feb 8, 2012 at 13:17

Gareth McCaughan · Accepted Answer · 2012-02-08 13:13:45Z

2

What you're missing is the difference between ++$level and $level+1. The former modifies the value of $level, so that further references to that variable in the same invocation of myfunction see the incremented value. If that's not what you want, write $level+1 instead.

answered Feb 8, 2012 at 13:13

Gareth McCaughan

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6 Comments

pufos Over a year ago

Genius ... I never understood that . Thank you very much , you saved my brains becaus I started to get frustrated.

pufos Over a year ago

It's the same way with arrays ? because I added an array to the function and when exits recursive mode ... the $array is not null anymore .. it was declared myfucntion($i, $condition = false, $array = null, $level = 0) ? Thank you very much

Gareth McCaughan Over a year ago

I think we'd need to see a bit more of the code to understand exactly what's happening with $array. Is there anything else that sets $array? Are there any other calls to myfunction that provide that fourth parameter?

pufos Over a year ago

the array is set if it met a condition and then function enters recursive mode with the array set, and when it end the recursivity , the array won't turn back to it's null value . I have describen in my question this (P.S)

Gareth McCaughan Over a year ago

Well, after you set $array explicitly, further uses of it in that invocation of myfunction -- e.g., in later iterations of that do-while loop -- will see the new value. Every time you call the function, you effectively get new versions of all its local variables (including the function arguments), which evaporate when the function returns. So: you call myfunction (call this Call 1). Its $array is null. It then sets $array to something else, and then calls myfunction again (call this Call 2). Its $array also starts out null. Then Call 2 returns, and back in Call 1 [... continued]

|

Karoly Horvath · Accepted Answer · 2012-02-08 13:13:23Z

2

Each executed function has its own local variables. As the name says, these variables are local, not shared between recursive calls.

the ++ operator increments the local variable.

answered Feb 8, 2012 at 13:13

Karoly Horvath

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3 Comments

Gareth McCaughan Over a year ago

I think what pufos is puzzled by is the fact that after the recursive call has returned, $level still has an increased value -- not the fact that separate calls to myfunction see different things. But the question isn't perfectly clear, so I may have misunderstood.

Gareth McCaughan Over a year ago

(Note: at the point when I wrote the above comment, yi_H's answer did not mention the fact that "the ++ operator increments the local variable".)

Karoly Horvath Over a year ago

yepp.. weird that SO doesn't show that the answer was edited.

codaddict · Accepted Answer · 2012-02-08 13:14:38Z

2

This is happening because you are doing ++$level which increments the local copy of $level and then passes the new incremented value to the recursive call of the function.

Try changing it to $level + 1 which just passes value of $value plus one to the function but does not change the local copy of the variable, so that if the function returns you still have the old un-incremented value in $value.

answered Feb 8, 2012 at 13:14

codaddict

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2 Comments

pufos Over a year ago

Thank you very much , that did the trick . But can you explai why ?

pufos Over a year ago

Ok I understood it clea now ... You are perfecty right and make sense.

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