Happy numbers were bring to the attention of Reg Allenby (a British writer and senior lecturer in pure mathematics at Leeds University) by his daughter, who had learned of them at school.

COMING SOON!

```
/* 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
#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;
}
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;
}
```