IsNumeric() Function

One thing you are responsible for as a programmer is, to the best of your ability, to validate data that is entered by the user. Data validation can take several forms.

• Testing for blank entry fields

• Testing for nonnumeric data

• Testing for values within acceptable ranges

• Testing for values that are within a predetermined set of values.
  

Testing for numeric values when numeric input is required is particularly necessary because programs may throw an error if nonnumeric data is entered when the program expects numeric data.

The IsNumeric() Function can be used to determine it a variable, constant or expression is numeric or not.

Format is

IsNumeric(variable, constant, or expression)

The function will return TRUE if the variable, constant, or expression evaluates to a number.

The function will return FALSE is the variable, constant, or expression does not evaluate to a number

For example

If IsNumeric(txtIncome.Text) = False Then

MsgBox("You must enter a valid number for income")

'Since the input was invalid I do not want any thing displayed in the output label

lblTax.Text = ""

Else.........

We will use the IsNumeric() function to validate numeric user input in all future labs. If the input which should be numeric is not numeric we will notify the user with an appropriate message.