Enforcing Minimum character length Validation(Minimum of 5 letters).

We will also use Asp.net RegularExpressionValidator control to achieve this task:-
Refer below code:-

<asp:TextBox Id = "txt_employee_code" runat = "server"></asp:TextBox>

<asp:RegularExpressionValidator Display = "Dynamic" 
ControlToValidate = "txt_employee_code" Id = "reg_ex_employee_code" 
ValidationExpression = "^[\s\S]{5,}$"  runat = "server" 
ErrorMessage = "Minimum of 5 letters allowed only">
</asp:RegularExpressionValidator>