output all possible combinations of N boolean variables

Does the solution need to be recursive?

amit, thanks but what happens when n=100?  I need to increase max chars, right?

ozo: no, not really... it just occurred to me when I thought out the process of how I would write it down, that my own process was sort of recursive.  In fact, if I could think of several ways to do it, I'd be even happier, so if you have non-recursive solutions, please show me!

Infinity: I did think of that (and in fact took out my poor attempt at it before posting the question).  

One of my goals was just to have this as one algorithm whose only input was "n".  So any char arrays and the like need to be self contained within the tf / outputCombos (whatever you want to call it) function.

My thought was to use a "static" array dynamically allocated based on the size of n.  But it's been quite a while since I've used C or done anything of this "academic" nature, that I couldn't even remember how to do that and when I looked it up, I didn't think it would work anyway.

If you choose only n=32, the program outputs 132 GB data.
For n=100 the program never ends.

Change the main to ...

int main()
{
      int HowMany = 3;
      char* Combo = new char[HowMany + 1];

      Combo[HowMany] = '\0';
      ouputCombos(HowMany, Combo);

      delete [] Combo;

      return 0;
}

and then there is no limit from program's side. However, the physical hardware and the time required would pose a practical limit.

>> One of my goals was just to have this as one algorithm whose only input was "n".  So any char arrays and the like need to be self contained within the tf / outputCombos (whatever you want to call it) function.

As you say, you could use either a static array within the recursive function or a global array.

Something along these lines :

void tf(int n) {
  static char *str = 0;
  static int pos = 0;
  static char *vals = "TF";
  int i;

  if (str == 0) str = (char*) calloc(n + 1, sizeof(char));

  for (i = 0; i < strlen(vals); i++) {
    str[pos++] = vals[i];
    if (n == 1) {
      fprintf(stdout, "%s\n", str);
    }
    else {
      tf(n - 1);
    }
    pos--;
  }
  return;
}

well, i did show complete code in the end heh ... but i'm sure you'll get something out of it :)

oh, and of course, don't forget to free() the allocated array !!!, ie. just before returning, check for pos == 0, and if so, free(). ie., place this line, just before the return statement :

  if (pos == 0) free(str);

>> If you choose only n=32, the program outputs 132 GB data.
>> For n=100 the program never ends.

I am aware that there will be 2^n combinations so the increase is quick, however the point was just to find a single algorithm that would take care of the problem for any n, regardless of space requirements (but hopefully find the best algorithm regarding time).

PaulCaswell- I'm interested in seeing the "print 'on the fly'" method you talked about if you have time in the afternoon =).

pallosp- can you explain your code a bit?  I've forgotten in particular what the left/right shift operators are doing and why you are using them.

I'm off to class and will be back tommorrow.  I thank you all for your help!