Entering Characters into Numeric Field

Question

Let's say I want to add two numbers with parameters num1 and num2. Now, I want to make sure the user does not enter characters or symbols. If they do I wan to throw an exception. Does anyone know how to do this?
declare
v_num1 number := p_num1;
v_num2 number := p_num2;
v_results number;
begin
if user enters an alphabetic field or symbol
raise error
else
v_results := v_num1 + v_num2;
...

Answer 1

No real application should be using SQL Plus as its user interface! And as I said in my first reply, it is no good assigning the values to the variables in the DECLARE section if you want to catch exceptions.
Here is some fully working code:
SET SERVEROUTPUT ON
ACCEPT p_number1 PROMPT 'Enter a number: '
ACCEPT p_number2 PROMPT 'Enter another number: '
DECLARE
  v_number1 NUMBER;
  v_number2 NUMBER;
  v_results NUMBER;
BEGIN
  v_number1 := '&p_number1.';
  v_number2 := '&p_number2.';
  v_results := v_number1 * v_number2;
  DBMS_OUTPUT.PUT_LINE('Result='||v_results);
EXCEPTION
  WHEN value_error THEN
    DBMS_OUTPUT.PUT_LINE('Invalid entry. ');
END;
/