Using a for loop:

bool anyPrime(int a, int b)
{
  for(int k = a; k <= b; k++)
  {
    if(prime(k)) return true;
  }
  return false;
}

Using a while loop:

bool anyPrime(int a, int b)
{
  int k = a;
  while(k <= b)
  {
    if(prime(k)) return true;
    k++;
  }
  return false;
}