how to determine whether a given number is prime or not?

Answer 1

#include <iostream>
using namespace std;

int main()
{
int n, i, flag=0;
cout << "Enter a positive integer: ";
cin >> n;
for(i=2;i<=n/2;++i)
{
if(n%i==0)
{
flag=1;
break;
}
}
if (flag==0)
cout << "This is a prime number";
else
cout << "This is not a prime number";
return 0;
}

Answer 2

Thanks a lot for your help...