Display Prime Numbers Between two Intervals

//Display Prime Numbers Between two Intervals
#include <iostream>
using namespace std;

int main()
{
    int start, num, end, i, flag;

    cout << "Enter two numbers(intervals): ";
    cin >> start >> end;

    cout << "Prime numbers between " << start << " and "
<< end << " are: ";

    while (start < end)
    {
        flag = 0;
num=start;
        for(i = 2; i <= num/2; ++i)
        {
            if(num % i == 0)
            {
                flag = 1;
                break;
            }
        }

        if (flag == 0)
            cout << num << " is a prime number\n ";

        ++start;
    }

    return 0;
}