This document discusses validating user input to ensure only numeric values are entered for variables that require numbers. It shows code for a program that asks the user for their favorite number. Initially, the code fails if a non-numeric value like "five" is entered instead of the number 5. The document then introduces the IsNumeric() function to check if the user input is a valid number before assigning it to the Integer variable. It demonstrates adding a While loop with IsNumeric() validation to prevent non-numeric values from being entered.

1. IS NUMERIC?
Just one way we can protect the user
from themselves!

2. Sometimes You want the user to
enter only numbers . . .
Module Module1
Sub Main()
Dim favouriteNumber As Integer
Console.WriteLine("What's your favourite number?")
favouriteNumber = Console.ReadLine()
Console.WriteLine("Your favourite number is " &
favouriteNumber)
Console.ReadLine()
End Sub
End Module

3. Sometimes You want the user to
enter only numbers . . .
If I enter the number 5, the program works

4. Sometimes You want the user to
enter only numbers . . .
If I enter five however, things start to break down

5. Sometimes You want the user to
enter only numbers . . .
BUT THAT
STILL MAKES
SENSE TO
ME!!

6. Sometimes You want the user to
enter only numbers . . .
Visual Studio is telling us there’s a InvalidCastException

7. Sometimes You want the user to
enter only numbers . . .
Visual Studio is telling us there’s a InvalidCastException
Visual Studio is telling us that it can’t put the word five
into the variable favouriteNumber

8. Remember, Variables have a specific
data type
Variables have a
I’m the type of data type
Variable that
holds only
Champagne !
Don’t you try
and put
Lemonade in
me!
Champagne
Bucket

9. Example data types
String
Integer
Double
Float
Champagne Char
Bucket
Boolean

10. You need to
protect the user
from
themselves . . .

11. You’re gonna need
some isNumeric
validation
protection . . .

12. !

13. isNumeric
We can use the isNumeric() function to tell if a
number entered by the user is a number
IsNumeric(temp)
The variable it will
check is a number

14. isNumeric
isNumeric() will return either true or false depending
on the input it is given

15. Adding isNumeric
Module Module1
Sub Main()
Dim favouriteNumber As Integer
Console.WriteLine("What's your favourite number?")
Dim temp As String
temp = Console.ReadLine()
While Not IsNumeric(temp)
Console.WriteLine("YOU HAVEN'T ENTERED NUMBER!")
temp = Console.ReadLine()
End While
favouriteNumber = temp
Console.WriteLine("Your favourite number is " & favouriteNumber)
Console.ReadLine()
End Sub
End Module

16. Adding isNumeric
The user has been stopped from entering the word five

17. Thanks!