Decimal to binary recursively?

[skanxalot]

I'm stuck. Can somebody help me with the algorithm to convert a decimal integer (0 - 1,000,000,000) to binary recursively? I know I'm going to %2 until it equals 0 or 1, but then what do I do?

[Cela]

#include <iostream>

using namespace std;

void dectobin(int x)
{
  if (x != 0)
  {
    dectobin(x >> 1);
  }

  cout<< !!(x & 1) <<flush;
}

int main()
{
  dectobin(5);
}

[skanxalot]

OK, you're reply didn't make much sense to me as I think I'm quite a bit behind you. I've just been learning recursion for a week now. This is what I know:

To find the binary of a decimal you do int division by 2 until it equals 1. Let's say I was doing the integer 9.

9 --- 1
4 --- 0
2 --- 0
1 --- 1

So the binary is 1001.

So for the recursive function my anchor or base is 1, right?

So I use this to call it again? Recursive_Function(number/2)

How then do I get the numbers off the stack to check for odd/even?

[Cela]

Okay, ultra simple without any bitwise operations. :-) What you do is recurse deeper as long as the number isn't 0, when it is you print the modulus of the number you have and return.

#include <iostream>

using namespace std;

void dectobin(int x)
{
  if (x != 0)
  {
    dectobin(x / 2);
  }

  cout<< x % 2 <<flush;
}

int main()
{
  dectobin(9);
}

The equivalent, more or less :-), with loops is like this

#include <iostream>
#include <vector>

using namespace std;

void printbin(int x)
{
  vector<int> bin;

  while (x != 0)
  {
    bin.push_back(x % 2);
    x = x / 2;
  }

  for (vector<int>::size_type i = 0; i < bin.size(); i++)
  {
    cout<< bin[i] <<flush;
  }
}

int main()
{
  printbin(9);
}

[skanxalot]

Cheers, mate!