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Evaluate equations on the DOS command line.
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Evaluate equations on the DOS command line.
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Contents of the NJEVAL.DOC file




Nifty James' Famous Expression Evaluator
Version 1.10 of 12 February 1989
(C) Copyright 1988, 1989 by Mike Blaszczak


THIS PROGRAM MAY NOT BE REDISTRIBUTED FOR PROFIT WITHOUT THE PRIOR
WRITTEN CONSENT OF THE AUTHOR. RESELLING OR PROVIDING THIS
PROGRAM AS AN INCENTIVE TO PURCHASE IS A CRIME.




Nifty James' Famous Expression Evaluator, or NJEVAL, is a program
designed to evaluate mathematical expressions. NJEVAL is a
"Command line calculator" for MS-DOS machines.

I wrote this program to avoid the irony of having a pocket
calculator next to my all-powerful IBM PC Compatible. I also
don't like the programmer's calculators which have saturated the
TSR market. There are too many TSR's as it is, and they all cause
a problem in one way or another.


Operation
----------

NJEVAL is very easy to use. Simply type the program's name,
NJEVAL, and follow it with a space. After that space, type the
expression you'd like to evaluate.

For example,

NJEVAL 35+9

would find the answer to 35+9, which is 44.

NJEVAL supports the four basic functions; addition,
multiplication, subtraction, and division. The syntax used is
very similar to that of the mathematics expressions used by most
modern computer languages and by most spreadsheet programs.

For example, to add two to eight and multiply that result by
thirteen, you would use:

NJEVAL (2+8)*13


Exponentiation
--------------

The operator precedence used is similar to most high level
languages, as well. Multiplication and division are "higher" than
addition and subtraction. Exponentiation, represented by the caret
(^) is lower than all four operators. You will find that you can
exponentiate values by using ** in place of the caret.

Thus, you can use:

NJEVAL 2**1/2

to find 2^0.5.

It should be noted, by the way, that this is a good way to find
roots. The program has no sqrt() or curt() functions. You may
recall from your math courses that, to find the y-th root of x,
you can do:

x^(1/y)

Of course, NJEVAL will complain if this results in a complex
number. For example, the result of the above is complex if x = -4
and y = 4.


Range
-----

NJEVAL uses the full "double" precision of the C language. Thus,
answers will be represented to a maximum of 16 digits to the right
of the decimal point.

Scientific notation can be used to enter your numbers. An example
is:

6.215e+12 is equivalent to 6.215 times 10 to the 12th power.


NJEVAL allows all numbers between 1.7E-308 and 1.7E+308.
Of course, the negatives of these numbers are also available. It
should be noted that NJEVAL doesn't check for overflows or
underflows. NJEVAL will, however, flag "digital math" no-no's,
such as division by zero and exponentiations resulting in complex
numbers.

To use these numbers, just write them as you would specify them in
a spreadsheet like 1-2-3 or in a program:

3.1415
0.1
-34
18.01
35e-2
6.2e+23


Modulo Division
------ --------

NJEVAL, as well as complementing the four functions with
exponentiation, allows the use of the modulo operator. This
operator provides the integral "remainder" of division. Since 5
divided by two is two remainder one, the command:

NJEVAL 5%2

will result in the answer 1.0.


Functions
---------

NJEVAL supports an extensive list of functions, as well.
Functions may be specified in either upper or lower case, and may
be abbreviated to as little as three characters. (Of course, if
the function name is one or two characters long, all characters
must be specified.)

These functions are supported by NJEVAL:

abs(x) - absolute value of x
acos(x) - arc cos of the angle x radians
acot(x) - arc cotangent of the angle x radians
acsc(x) - arc cosecant of the angle x radians
asec(x) - arc secant of the angle x radians
asin(x) - arc sine of the angle x radians
atan(x) - arc tangent of the angle x radians
cos(x) - cosine of the angle x radians
cot(x) - cotangent of the angle x radians
csc(x) - cosecant of the angle x radians
deg(x) - convert x radians to degrees
exp(x) - e to the power of x
fact(x) - factorial of x
ln(x) - natural (base e) logarithm of x
log(x) - base 10 logarithm of x
pi(x) - pi times x
rad(x) - converts x degrees to radians
sec(x) - secant of the angle x radians
sin(x) - sine of the angle x radians
tan(x) - tangent of the angle x radians

If any of these functions are passed invalid values, NJEVAL will
abort with an error. The arc-trig functions, for example, cannot
accept values outside of the closed interval [0,1].

NOTE: NJEVAL computes all trig functions [sin(x), etc.] using
radians for the variable. If you want to use degrees in a
variable, use the rad(x) function to convert degrees to radians.
For example, to calculate the sine of 30 degrees, you would enter:

sin(rad(30))

Using these functions is similar to any other high level language.
The function name and its ending left parenthesis function as an
opening parenthesis in the precedence of the evaluation. Thus:

sin(.7)^2+cos(.7)^2

would evaluate to 1.0. You may find that certain identities don't
evaluate to what you would expect them to. This is because of the
limits of precision in computer math when dealing with irrational
numbers. While the sin^2+cos^2 identity almost always works, the
sec^2-tan^2 identity usually doesn't work, for example.

Along with this problem, another comes. For example:

sec(0.5*pi)

is undefined. However, NJEVAL will evaluate

sec(pi(0.5))

to be a very (very) large number. This is again because of the
rounding errors in binary math. It is a good approximation,
considering:

lim (sec(x)) == +infinity
x -> 0.5+


Sending Results to a File or the Printer
-----------------------------------------

You'll notice that NJEVAL prints a message each time it makes a
calculation. You may want to send your calculations to the
printer or to a file for future reference. The message is not
sent to the file or printer.

To send a calculation to the printer or a file, use the DOS
redirection character. The following are valid:

NJEVAL 2+3 >PRN Sends the result to the printer on LPT1:
NJEVAL 2+3 >CALCS.TXT Sends the result to the file, CALCS.TXT.
NJEVAL 2+3 >>CALCS.TXT Adds the result to the file, CALCS.TXT.

Naturally, you can include any path or drive data to the file
specification for redirection. Remember that a single
redirection character (>) will open a new file, overwriting any
file with the same name, so use caution here.


How NJEVAL Works
-----------------

This section briefly describes the innards of NJEVAL. Skip it if
you're not interested; it isn't required reading.

NJEVAL operates by evaluating the expression on the command line.
NJEVAL first assembles all the argv[] strings into one giant
string. This is simply because it is more convenient to chop up
the string than to step through all the information in the argv[]
list.

NJEVAL then takes this string and breaks off tokens. The tokens
are kept in a doubly linked list. Each number, operator, function
name, and parenthesis is kept in an entry in this list. NJEVAL
uses three variables to keep track of which tokens are valid. For
example, one binary operator can't follow another. So, when
NJEVAL finds a binary operator, it sets the flags so that, if the
next term is binary operator, an error will be generated.

Here, the real work starts.

NJEVAL surrounds the original expression with an additional set of
parentheses. This little trick allows the heart of the operation
to go more smoothly.

NJEVAL looks for the rightmost opening parenthesis on the line.
In the example:

(35+15-2)/(2*(3+7))

the rightmost left parenthesis is in the denominator, just before
the three and just after the multiplication.

NJEVAL then looks for the matching right parenthesis. In the
above example, it's after the seven which follows the addition in
the denominator.

NJEVAL uses these parentheses as starting and ending points.
Starting with the left parenthesis, NJEVAL works towards the
right. If it finds an operator having a greater precedence than
the other operators that were found, NJEVAL remembers its
position.

Once it reaches the right parenthesis, NJEVAL then evaluates the
term containing the operator with the most precedence. It
replaces the operator and its operands with the result of that
operation. So, the above example would become:

(35+15-2)/(2*(10))

Since (10) is perfectly simplified, NJEVAL erases the surrounding
parentheses, yielding:

(35+15-2)/(2*10)

The process then repeats leaving:

(48/20)
or
2.4

NJEVAL prints this result and terminates.



Registration
------------

I'm very proud of NJEVAL as a program. It evolved relatively
smoothly, when time permitted, and was fun to develop. I think
the code is graceful and well written.

If you find NJEVAL of 'educational' value, or find that it is
useful to you, please register your copy. Registration guarantees
you a thank you letter from me, as well as a list of other
program's I've released. If you have any questions about
anything, I'll be more likely to answer them if you enclose a
check. Questions about assembly language are my forte, while
questions about relationships aren't. Please use your judgment.

I used to be a starving high school student, and now I'm a
struggling college student with a full-time job. My 'recommended'
price for the program is $10, however.


Mike Blaszczak
35 Ginger Lane #229
East Hartford, CT 06108
(203)-568-2700

If you decide to write or register, PLEASE be sure to let me know
what version of which program you have. This will allow me to
better determine if you need to receive an update diskette.


Hindsight 20/20
---------------

Thanks to Mike Todd for his "IBMSIG Gold Card" Service. He found
a problem with DOS Versions earlier than 3.00. He also puts up
with my persistent releasing of "new versions". The fix for the
bug he found, as well as a problem with the getnumber() routine
and scientific notated numbers was the cause for version 1.01.
Version 1.00 was never released to the public.

A big THANK YOU to everyone who will register this program and
everyone who has registered my other programs! Today, I got a
"cheque" from England. I was pretty impressed, I mean to tell you.
Thanks!



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