Sum of Prime/NonPrime numbers

# include <iostream>
using namespace std;
#include <iomanip>
#include <math.h>
#include <cmath>
#include <string>

int main()
{
    string number;
    int sumPrime = 0;
    int sumNonPrime = 0;
    int tempnumber;

    while (number != "stop") {
        cin >> number;
        if (number == "stop") {
            break;
        }
        tempnumber = stoi(number);
        if (tempnumber < 0) {
            cout << "Number is negative." << endl;
        }
        else {
            bool isPrime = true;
            int i = 2;
            while (i <= tempnumber / 2)
            {
                if (tempnumber % i == 0) {
                    sumNonPrime += tempnumber;
                    isPrime = false;
                    break;
                }
                i++;
            }
            if (isPrime) {
                sumPrime += tempnumber;
            }
        }
    }
    cout << "Sum of all prime numbers is: " << sumPrime << endl;
    cout << "Sum of all non prime numbers is: " << sumNonPrime << endl;

    return 0;
}