As a "programmer", programming is solving problems.
There are several ways to "validate" user input. Here are two:
1. To disallow invalid input as it is entered - the TextBox's KeyDown event and block invalid value. For example:
private void txtSomeField_KeyDown(object sender, KeyEventArgs e)
{
e.SuppressKeyPress = e.KeyValue < 34 || e.KeyValue > 127;
}
2. Only enable the SAVE/OK/etc... button if the input is valid
The third option is to check the user input after the SAVE button is pressed.