static bool isHappy (int n) {
   if(n<=0)  return false;
   Set<int> previouslySeen;
   while (n>1 && !previousySeen.contains(n)) {
      previouslySeen.add(n);
      n = completeSumOfSquaredDigits(n);
   }
   return n==1;
}

static bool isHappy(int n) {
   if(n<=0)  return false;
   Set<int> endpoints; 
   endpoints += 1,4,16,37,58,89,145,42,20;   // comma operator makes endpoints all the numbers and only 
                                                                                //these numbers
   while(!endpoints.contains(n))  {
      n=computeSumOfSquaredDigits(n);
   }

   return n==1;
}

Let you define data structures without being all hardcore classes/object orientated programming

Exactly the same as classes except for default privacy (struct has default of public)

struct fraction {
   int numerator;
   int denominator;
}

bool operator < (const fraction& one, const fraction & two)  {
   return one.numerator*two.denominator < one.denominator * two.numerator;
}