Check Whether a Number can be Express as Sum of Two Prime Numbers using c++

This program takes a positive integer from user and checks whether that number can be expressed as the sum of two prime numbers. If that number can be expressed as sum of two prime numbers then, that number is expressed as sum of two prime numbers in output. To perform this task, a user-defined function is created to check prime number.

#include <iostream>
using namespace std;
int check_prime(int n);
int main()
{
    int n, i, flag=0;
    cout << "Enter a positive  integer: ";
    cin >> n;
    for(i=2; i<=n/2; ++i)
    {
        if (check_prime(i)==0)
        {
            if ( check_prime(n-i)==0)
            {
                cout << n << " = " << i << " + " << n-i << endl;
                flag=1;
            }

        }
    }
    if (flag==0)
      cout << n << " can't be expressed as sum of two prime numbers.";
    return 0;
}
int check_prime(int n) /*check prime number*/
{
  int i, flag=0;
  for(i=2;i<=n/2;++i)
  {
      if(n%i==0)
      {
          flag=1;
          break;
      }
  }
  return flag;
}

Output

Enter a positive integer: 34
34 = 3 + 31
34 = 5 + 29
34 = 11 + 23
34 = 17 + 17