Introduction

In this article I have explained input validation using the Char.IsLetter( ) method and the Char.IsNumber( ) method.

Char.IsLetter( )

The Char.IsLetter() function allows us to determine if a character is a Unicode letter. If the specified character is a letter then the function Char.IsLetter returns true else returns false.

Syntax :

if (Char.IsLetter(Convert.ToChar(nametxtbox.Text.Chars(0)))) then

Char.IsNumber( )

The Char.IsNumber( ) function determines that a char is a numeric Unicode. IsNumber() is an overloaded function of the Character class. The Character class wraps a value of the primitive type, char, in an object. An object of type Character contains a single field whose type is char. If the specified character is a number then the function Char.IsNumber() returns true else returns false. It can evaluate the type double number and is not restricted to the single character.

Syntax:

if (Char.IsNumber(Convert.ToChar(nametxtbox.Text.Chars(0)))) then

Now I want to show you how to use Char.IsLetter() and Char.IsNumber() functions in a Windows Forms appliation. Let's use the following procedure.

Step 1:

Open Visual Studio then select "Create New Project" --> "F# Console Application".

CreateApplication

Step 2:

Now go to the Solution Explorer on the right side of the application. Right-click "References" then select "Add references".

SelectReferences


addref

Step 3:

After selecting "Add References", in the framework template you need to select "System.Windows.Forms" and "System.Drawing" while holding down the Ctrl key and Click on "Ok."

ImortNamespaces

Step 4:

Write the following code in the F# editor:

open System

open System.Windows.Forms

open System.ComponentModel

open System.Drawing

let valform = new Form(Text="Input Validation")

let lblname=new Label(Top=20,Left=20)

let nametxtbox=new TextBox(Top=20,Left=120,Width=120)

let okbutton=new Button(Top=70,Left=80)

let exitbutton=new Button(Top=70,Left=170)

lblname.Text<-"Enter a name :"

exitbutton.Text<-"Exit"

okbutton.Text<-"Ok"

valform.Controls.Add(exitbutton)

valform.Controls.Add(okbutton)

valform.Controls.Add(lblname)

valform.Controls.Add(nametxtbox)

okbutton.Click.Add(fun ok->

if (Char.IsLetter(Convert.ToChar(nametxtbox.Text.Chars(0)))) then

MessageBox.Show(nametxtbox.Text+" "+"is valid name", "Letter Validation",MessageBoxButtons.OKCancel, MessageBoxIcon.Information)|>ignore

if (Char.IsNumber(Convert.ToChar(nametxtbox.Text.Chars(0)))) then

MessageBox.Show(nametxtbox.Text+" "+ "invalid name", "Num Validation",MessageBoxButtons.RetryCancel, MessageBoxIcon.Warning)|>ignore)

exitbutton.Click.Add(fun exit->valform.Close())

Application.Run(valform)

Step 5:

Debug the application by pressing F5 to execute the Windows Forms application. After debugging the application, you will get a Windows Forms application as in the following figure.

AfterDebug

Step 6:

Enter a name starting with any letter.

EnterName

Step 7:

Press the "Ok" button to determine if the name is valid or invalid.

OkButton

Step 8:

The name you entered is valid because the name starts with the letter.

LetterValidation

Step 9:

Enter a name starting with a numeric.

EnterNameStartWithNum

Step 10:

Now just click on the "Ok" button to validate the TextBox.

InvalidName

Summary

In this article we explained the Char.Isletter() and Char.IsNumber() and validate the textboxes using these two functions in Windows Forms application.