I'm developing a web application using Ethereum SmartContract.
And I have a question.

I want to add a address to array of addresses without duplication.
But I can't do without duplication.
It adds all address evenif array contains same value.
Below is code.

```
function addTokenHolder(address _tokenHolder) returns (bool success) {
  uint len = tokenHolders.length;
  for(uint i = 0; i > len; i++) {
    if (tokenHolders[i] == _tokenHolder) return false;
  }
  tokenHolders.push(_tokenHolder);
  return true;
}

```

Please advise.