The program uses numbers and symbols together in much the same
 way as an algebraic calculator.  A number may be entered these ways:

     123      - as an integer (up to 16 digits).
    -123      - any value may be signed.
    1.23      - as a decimal (up to 16 significant digits).
    (1.2E+3)  - as a power.  NOTE: THE POWER NOTATION MUST BE ENCLOSED
                                   IN PARENS EACH TIME IT IS USED!!

 The following operations are defined:

    +  addition.
    -  subtraction.        NOTE: The only time two operators can be next
    *  multiplication.     to each other is when one is the '=' operator.
    /  division.           10^-2 is not legal - you should type 10^(-2),
    ^  exponentiation.     but X=-2 is legal).
    %  modulus
    =  assignment.

 You may define and use variables up to 30 characters in length.
 If you use variables just make sure that they are unique, in other
 words that they aren't already being used as program defined function
 or constant names (like PI, SIN, LOG).  The variable name must begin
 with a letter, otherwise results are not well defined.

 At the VaxCalc> prompt you may enter any of the following:

  1. Any valid expression -  SIN(10^1.2-LOG(PI))
  2. Assign the value of an expression to a variable - X=2*PI

 Parens are used to define the order of computation.
 2+3*4 is not the same as (2+3)*4: 2+3*4 = 14, while (2+3)*4 = 20.

 The arguments for all functions MUST be enclosed in parens -
 for example SIN(PI/2).

 The arguments for all normal trig functions are in RADIANS.

 The DEG function converts RADIANS to DEGREES.   So, if you want
 the angle whose SIN is 1 in degrees, you enter DEG(ARCSIN(1)).