Using a for loop:

int sumPrimes(int n)
{
  int sum = 0;
  for(int k = 2; k <= n; k++)
  {
    if(prime(k)) sum = sum + k;
  }
  return sum;
}

Using a while loop:

int sumPrimes(int n)
{
  int sum = 0;
  int k = 2;
  while(k <= n)
  {
    if(prime(k)) sum = sum + k;
    k++;
  }
  return sum;
}