1. Load the Visual Basic 6.0 environment by clicking the program's shortcut icon from the desktop, or selecting "Microsoft Visual Basic 6.0" from the "Start" menu in your computer.

2. Select "Standard EXE" from the "New Project" dialog box, then click "Open" button.

3. Add a text box into the form by clicking the "TextBox" control from the "Toolbox," then drawing the desired text box size. Make sure it's wide enough to hold input characters from the user.

4. Clear the text caption by erasing the word "Text1" next to the "Text" property at the "Properties" window on the right side of the screen.

5. Double-click the text box control to display the "Code" window. This is where you'll write the instructions or source codes that the program will execute at run-time. The source code you are going to write will validate user input and accepts only numeric characters, else it will display an error message.

6. Insert the following code within the "Text1_Change" event:

   If Not IsNumeric(Text1.Text) Then

   MsgBox "Numeric input only!", vbCritical, "Invalid Input"

   Text1.Text = ""

   End If

7. Press F5 or select "Run" then "Start" from the menu to switch to runtime-mode.

8. Test the program to check that it's running as it should. Type alphanumeric characters or combination of letters and numbers into the text box. You should see an error message letting you know the input is invalid. Now, type only numbers into the text box. If no error message pops up, the program is running correctly.

9. Save the program by selecting "Save Project" from the "File" menu. Provide a filename into the space provided, then click "Save."

In code textbox_key_press

if keyascii <48 or keyascii >57 then

keyascii=0

end if