Eratosthenes

private void button1_Click(object sender, EventArgs e)
        {
            int max = int.Parse(textBox1.Text);
            int[] primzahlen = new int[max-1];
            for (int i = 0; i < max-1; i++)
            {
                primzahlen[i] = i + 2;
            }
            int bigprime = 2;
            while (bigprime * bigprime < max){
                for (int i = bigprime*2-2; i < max - 1; i += bigprime){
                    primzahlen[i] = 0;
                }
                for (int i = bigprime-1; i < max -1; i += 1){
                    if (primzahlen[i] != 0 && isprime(primzahlen[i])) {
                        bigprime = primzahlen[i];
                        break;
                    }
                }
            }
            for(int i = 0; i < primzahlen.Length; i++){
                if (primzahlen[i] != 0) {
                    listBox1.Items.Add(primzahlen[i]);
                }
            }


        }