//1
    int n = 12345, sum = 0;
    while(n) {
        sum+=n%10;
        n/=10;
    }
    cout << sum; //15
//2
    int n = 12345, sum = 0;
    for (sum = 0; n > 0; sum += n % 10, n /= 10);
    cout << sum; //15