IsNumeric Function (VB Work-A-Like)

Modified on 2021/02/07 18:36 by CaptainBoing — Categorized as: Console, Maths, Strings

This function is inspired by the VB function of the same name. It is smaller in scope in that only simple numeric notation is supported. It will test validity for both integer (opt=0 or absent) and decimal number strings (opt<>0).

It is intended for use where an arbitrary input must be forced into numeric compliance. It does not sanitize the string (out of scope for a small building block), rather providing an indication if the argument is/not compliant.

Usage:
=IsNumeric(MyString,Option)

Examples:
x=IsNumeric("345")
If Not IsNumeric(a$,1) Then Print "Not a Number"

Caveats:
The string cannot be blank ""
No support for scientific notation e.g. 1.78E+34
The Function tests the input string for numeric compliance, it does not guarantee conversion to any numeric data-type, i.e. Val().
White space must be pre-trimmed as required.

Dependencies:
None

The Code:

'Test a string as numeric. opt=1 allows decimals
	Function IsNumeric(a$,opt As Integer) As Integer
		If a$="" Then Exit Function
		Local Integer n,Dots
		Local q$,c$
		If opt Then q$=" 0123456789." Else q$=" 0123456789"
		For n=1 To Len(a$)
			c$=Mid$(a$,n,1)
			If Instr(q$,c$)<2 Then Exit Function
			Dots=Dots+(c$=".")
		Next
		IsNumeric=(Dots<=1)
	End Function

The following is an alternative function that uses regular expressions to perform an identical function. The overhead of the regexp parser is considerable and this version is probably best avoided unless you are using regular expressions elsewhere in your code.

Dependencies:
Regular expressions.

Caveats:
Much smaller function but slower execution due to overhead of regular expressions. A good companion if you are already using regexps (IsDate/IsTime) in your code

The Code:

'Test a string as numeric using regular expressions. opt=1 allows decimals
	Function IsNumeric(a$,opt As Integer) As Integer
		If a$="" Then Exit Function
		Local q$
		If opt Then q$="^[0123456789]*\.?[0123456789]*$" Else q$="^[0123456789]*$"
		IsNumeric=RegExp(q$,a$)
	End Function