```
if(textBox1.TextLength !=10)
{
    MessageBox.Show("Wrong Telephone No Please check it again",
                    "ERROR",MessageBoxButtons.OK,MessageBoxIcon.Information);
}   

```

I try this code for validate text box for telephone number in c# .I assume that user must enter 10 numbers.But this didn't work correctly. This code allows digits and also characters. How can I validate text box that allows only 10 digits & only digits.