document happy numbers

others/happy_number.cpp

@@ -1,28 +1,39 @@
-/* A happy number is a number whose sum of digits is calculated until the sum is a single digit,
-  and this sum turns out to be 1 */
-
-// Copyright 2019 TheAlgorithms contributors
+/**
+ * A [happy number](https://en.wikipedia.org/wiki/Happy_number) is a decimal
+ * number whose sum of digits is calculated until the sum is a single digit, and
+ * this sum turns out to be 1.
+ */
 
 #include <iostream>
 
-int main() {
-  int n, k, s = 0, d;
-  std::cout << "Enter a number:";
-  std::cin >> n;
-  s = 0;
-  k = n;
-  while (k > 9) {
-    while (k != 0) {
-      d = k % 10;
-      s += d;
-      k /= 10;
+/**
+ * Checks if a decimal number is a happy number
+ * \returns true if happy else false
+ */
+template <typename T>
+bool is_happy(T n) {
+    T s = 0;              // stores sum of digits
+    while (n > 9) {       // while number is > 9, there are more than 1 digit
+        while (n != 0) {  // get digit
+            T d = n % 10;
+            s += d;
+            n /= 10;
+        }
+        n = s;
+        s = 0;
     }
-    k = s;
-    s = 0;
-  }
-  if (k == 1)
-    std::cout << n << " is a happy number" << std::endl;
-  else
-    std::cout << n << " is not a happy number" << std::endl;
-  return 0;
+    return (n == 1) ? true : false;  // true if k == 1
+}
+
+/** Main function */
+int main() {
+    int n;
+    std::cout << "Enter a number:";
+    std::cin >> n;
+
+    if (is_happy(n))
+        std::cout << n << " is a happy number" << std::endl;
+    else
+        std::cout << n << " is not a happy number" << std::endl;
+    return 0;
 }