跪求大仙们解释...

private void button3_Click(object sender, EventArgs e)
        {
            string str = textBox1.Text;
            if ((str.Length/2) == 0)
            {
                textBox4.Text = str;
            }
            else
                MessageBox.Show("请输入偶数位个数");
        }
为什么不论我输入偶数个数据还是奇数个数,它都弹框啊.