public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{
String aString = textBox1.Text;
if (aString.Any(Char.IsLetter) && aString.Any(Char.IsDigit))
MessageBox.Show("You cannot pass letters and numbers at the same time.");
}
}