Happy numbers in C+- Each new sum-of-sqared-digit is saved in an open array to check for it not being repeated. Finish either when repeated or when this sum is 1

happynumbers.cpp

// happynumbers.cpp
// juanfc 2019-01-02
//

#include <iostream>
#include <array>
using namespace std;

struct TOpenVec {
    int n;
    array<int, 500> ar;
};


bool isHappy(int n);

int main()
{
    for (int i = 1; i <= 3000; ++i) {
        if (isHappy(i)) {
            cout << i << ", ";
        }
    }
    cout << endl;
    return 0;
}

int sumSqDigits(int n);
bool in(int n, TOpenVec prev);

bool isHappy(int n)
{
    TOpenVec previous = {0, {{}}};
    while ( (n = sumSqDigits(n)) != 1 and not in(n, previous))
        previous.ar[previous.n++] = n;
    return not in(n, previous);
}

bool in(int n, TOpenVec prev)
{
    int i = 0;
    while (i < prev.n and n != prev.ar[i])
        ++i;
    return i < prev.n;
}


int sumSqDigits(int n)
{
    int s = 0;
    while (n > 0) {
        int lastDig = n % 10;
        s += lastDig * lastDig;
        n /= 10;
    }
    return s;
}