To determine if a number is a happy number, you would typically use a while loop. This is because you need to repeatedly calculate the sum of the squares of the digits of the number until you either reach 1 (indicating that it is a happy number) or enter a cycle that leads to 4 (indicating that it is an unhappy number).
Using a while loop allows you to continue this process until one of the two conditions is met.
Thus, the correct response is:
while loop