Adding GameObject to GameObject[] array

Hello everyone, thank you for your time.

Quick question, I've been looking at code for almost 8 hours in a row and I just can't tell on such small errors. Correct me if Im wrong but. Im trying to do something similar.

Im trying to get every element inside an array(gameObject) that matches certain criteria. If it does, it goes inside the newElement. Like this!

 public GameObject[] newArray;
 public GameObject[] oldArray; //This array is set on the inspector. (Dragged the GO's inside)
 
 Start(){
 int tempCounter;
 
 for(cnt=0;cnt<= oldArray.Length;  cnt++){
 
     if(matches Criteria){
          newArray[tempCounter] = oldArray[cnt];
         tempCounter++;
     }
 }
 
 }
 

But I keep getting a IndexOutOfRange error.

I don't think i have to hardcode the size of the array, do I?(It's because the size of the array depends on wether it matches the criteria or not.... Yes. I've checked that both, the array and the item are gameobjects....

Help? Please...The coffee is just not doing its job anymore. Thank you for your help and time!