Strange behavior converting data types?

Using Arduino Programming Questions
#1

I’m writing a function to convert a number to trinary.
The function receives an integer and puts appropriate values into a global array of integers. I’ve written three different functions that I think should do the same thing, but they don’t for the numbers 26 and 27. I’d like help figuring out why. I suspect it has something to do with data types.

First, the function that works.
void inTrinary(int n){
ledState[0] = (int(n/(pow(3,0)))%3);
ledState[1] = (int(n/(pow(3,1)))%3);
ledState[2] = (int(n/(pow(3,2)))%3);
ledState[3] = (int(n/(pow(3,3)))%3);
ledState[4] = (int(n/(pow(3,4)))%3);
ledState[5] = (int(n/(pow(3,5)))%3);
}

if n = 26, then ledState = {2, 2, 2, 0, 0, 0} and
if n = 27, then ledState = {0, 0, 0, 1, 0, 0}

Second, one function that doesn’t work.
void inTrinary(int n){
for (int j = 0; j < 6; j++){
ledState[j] = (int(n/(pow(3,j)))%3);
}
}

for this function, if n = 27, then ledState unfortunately = {0, 2, 0, 1, 0, 0}

Third, another function that doesn’t work.
void inTrinary(int n){
for (int j = 0; j < 6; j++){
ledState[j] = ((n/int(pow(3,j)))%3);
}
}

for this function, if n = 26, then ledState unfortunately = {2, 2, 2, 1, 0, 0}

If someone could explain to me why there’s this difference, I’d greatly appreciate it. Thank you.

#2

From what I have read elsewhere, it seems that pow() does not give exact results, and that is causing the problem. Or maybe it's floating-point division, I don't know.

Use this in your code:

int myPow(int x, int y) {
  // raises x to the power of y
  int z = 1;
  while (y--) {
    z *= x;
  }
  return z;
}

Then, everywhere your code uses pow(), change it to myPow(), and everything should be OK. (Untested code, please let me know if any problems.)

#3

You probably should avoid pow() altogether, something more efficient like:

void inTrinary(int n)
{
  for (int j = 0; j < 6; j++)
  {
    ledState[j] = n % 3 ;
    n /= 3 ;
  }
}
#4