Oracle function:
FUNCTION Is_Numeric(Parameter_ IN VARCHAR2) RETURN NUMBER IS

char_ VARCHAR2(1);
char_counter_ INTEGER;
is_numeric_ NUMBER;

BEGIN

is_numeric_ := 1;
char_counter_ := 0;
WHILE (char_counter_ <= LENGTH(Parameter_)) LOOP
char_counter_ := char_counter_ + 1;
char_ := SUBSTR(Parameter_,
char_counter_,
1);
IF (INSTR('0123456789',
char_,
1) = 0) THEN
is_numeric_ := 0;
EXIT;
END IF;
END LOOP;

RETURN(is_numeric_);
END Is_Numeric;

VB.NET code to run this function:

Imports System.Data.OracleClient
Imports System

Module ModuleTest

Const _oracleuser As String = "oracle user>"
Const _connectstring As String = "Oracle connect string"
Public Class TEST_API

' FUNCTION Is_Numeric(Parameter_ IN VARCHAR2) RETURN NUMBER IS
Public Function IsNumeric(ByVal Parameter_ As String) As Decimal
Dim _return_value As Decimal
Dim _commandtext As String = _oracleuser + ".TEST_API.Is_Numeric"
Using connection As New OracleConnection(_connectstring)
Dim Cmd As New OracleCommand(_commandtext, connection)
Try
Cmd.CommandType = CommandType.StoredProcedure
Cmd.Parameters.Add("Parameter_", OracleType.VarChar).Direction = ParameterDirection.Input
Cmd.Parameters.Add("Return_Value_", OracleType.Number).Direction = ParameterDirection.ReturnValue
Cmd.Parameters("Parameter_").Value = Parameter_
connection.Open()
Cmd.ExecuteNonQuery()
_return_value = Cmd.Parameters("Return_Value_").Value
Catch ex As Exception
MessageBox.Show("Oracle error message: " + ex.Message)
Return (-1)
Finally
connection.Close()
End Try
End Using
Return (_return_value)

End Function
End Class

End Module