CODEWITHSUNDEEP
javarecursion
Grammin
Grammin

Reputation: 12205

Global variable in a recursive function how to keep it at zero?

So if I have a recursive function with a global variable var_:

int var_;

void foo()
{
  if(var_ == 3)
    return;
  else
    var_++; foo();
}

and then I have a function that calls foo() so:

void bar()
{
  foo();
  return;
}

what is the best way to set var_ =0 everytime foo is called thats not from within itself. I know I could just do:

void bar()
{
  var_ =0;
  foo();
  return;
}

but I'm using the recursive function a lot and I don't want to call foo and forget to set var_=0 at a later date.

Does anyone have any suggestions on how to solve this?

Thanks, Josh

Upvotes: 2

Views: 2358

Answers (5)

Goblin Alchemist
Goblin Alchemist

Reputation: 827

To let the function know whether it was called from within itself, you can add a parameter:

int var_;

void foo(boolean from_itself)
{
 if(!from_itself)
  var_ = 0;
 if(var_ == 3)
  return;
 else
  var_++; foo(true);  // from within itself
}

void bar()
{
 foo(false);  // not from within itself
 return;
}

So this approach doesn't require adding a helper function.

Upvotes: 1

axtavt
axtavt

Reputation: 242686

Do you actually need this global variable?

If it's used only to control the depth of recursion, you can rewrite it in more elegant way, as follows:

void foo()  {
    fooHelper(0);
}

void fooHelper(int var) {
    if (var == 3) return;
    else fooHelper(var + 1);
}

Upvotes: 1

Costi Ciudatu
Costi Ciudatu

Reputation: 38195

To add to the first two (amazingly similar) answers that you got, make only the foo() method visible from outside your class and keep the foo_helper() / foo_recur() as private (the var_ should also be private). If this is meant to be used in a multi-threaded environment, you should also make foo() synchronized.

Also, it's better to call "var_" an instance- or class- variable (instead of "global").

Upvotes: 1

Ned Batchelder
Ned Batchelder

Reputation: 375574

I would split foo() into an initializing function, and the true recursive function:

void foo()
{
    var_ = 0;
    foo_recur();
}

void foo_recur()
{
  if(var_ == 3)
    return;
  else
    var_++; foo_recur();
}

Upvotes: 3

LoveAndCoding
LoveAndCoding

Reputation: 7947

Turn foo() into a helper function.

void foo() {
    var_ = 0;
    foo_helper();
}

void foo_helper() {
    if(var_ == 3)
        return;
    else
        var_++; foo_helper();
}

You won't have to change any existing code, and you can still just call foo() and let it do its work.

Upvotes: 6

Related Questions