Решение двух задач на циклом While

Task1: Check whether a given number is a prime
unsigned short int A, Divisor = 2;
std::cout <>"; std::cin >> A ;
while (A % Divisor != 0)
Divisor++;
if (Divisor == A)
std::cout << A << " is prime number";
else std::cout << A << " is not prime number";
Question 1: What error will be if a user enters 1?
Question 2: How to fix this error?
Task2: Count and output sum of digits in entered number
1. Code it
2. Test the program
1. Sum for 1000 is 1
2. Sum for 14 is 5
3. Sum for 0 is 0
4. Sum for 12345 is 15
Last digit of number — it's reminder on dividing by 10
Rest digits of number — it's result of integer division by 10
int r = a % b; int i = (int)a / b;