Help with Java Calculator Program

[DeAndrea Monroe]

I am writing a calculator program in Java. I just need the basics but
I'm using a stack. I'm trying to do a nested while loop that counts
integers that are greater than 9 but I can't seem to get it right. My
code can be found here: http://code.google.com/p/cschelp/source/list

 

[Stefan Ram]

I'm trying to do a nested while loop that counts integers
that are greater than 9 but I can't seem to get it right.

for( counter.reset(); integers.hasNext(); )
if( integers.getNext().isGreaterThan( 9 ))counter.increment();

»Besides a mathematical inclination, an exceptionally
good mastery of one's native tongue is the most vital
asset of a competent programmer.«

Edsger Wybe Dijkstra

 

[DeAndrea Monroe]

for( counter.reset(); integers.hasNext(); )
if( integers.getNext().isGreaterThan( 9 ))counter.increment();

      »Besides a mathematical inclination, an exceptionally
      good mastery of one's native tongue is the most vital
      asset of a competent programmer.«

    Edsger Wybe Dijkstra

Thanks so much.

 

[DeAndrea Monroe]

On Oct 27, 9:37 am, (e-mail address removed)-berlin.de (Stefan Ram) wrote:

I'm having problems with that code working.

 

[Stefan Ram]

I'm having problems with that code working.

It assumes appropriate types of »counter« and »integers«.
Thus, the operations »reset()«, »hasNext()«, »getNext()«,
»isGreaterThan( 9 )« and »increment()« usually still need to
be implemented.

 

[DeAndrea Monroe]

I am now getting many errors pertaining to my code. Most of the errors
say; class, interface, or enum expected. I thought I made classes for
everything that's being used. I also made a package for
calculatorEngine, but I'm still getting errors there.

 

[DeAndrea Monroe]

You may not be going at this the best way.

I usually start a program by writing something very simple that does a
tiny subset of the required behavior, and is only a dozen lines or so.

The code was given to me in a C++ format, I was just supposed to
change a few things and make it work with Java. The functions and what
they do are recognizable but I just can't get them to actually do what
is stated.

 

[DeAndrea Monroe]

The code was given to me in a C++ format, I was just supposed to
change a few things and make it work with Java. The functions and what
they do are recognizable but I just can't get them to actually do what
is stated.

I made a few changes to the code and I'm still getting the same
errors. Is there a way where I can compare C++ code to Java code?

 

[Martin Gregorie]

I made a few changes to the code and I'm still getting the same errors.
Is there a way where I can compare C++ code to Java code?

Use the mark 1 eyeball?

More seriously, I've converted C to Java by duplicating the source and
editing it so that:
- all globals become class attributes
- functions become methods
- constant definitions in the header file get rolled into the class
as public static final attributes
- other changes made as needed

but this does depend for its success on the semi-OO way I've always
written C, in which a source file, which contains functions and all the
globals that are used by them has a vague resemblance to a class.

 

[Stefan Ram]

It assumes appropriate types of »counter« and »integers«.
Thus, the operations »reset()«, »hasNext()«, »getNext()«,
»isGreaterThan( 9 )« and »increment()« usually still need to
be implemented.

Just for fun, here is a complete program with the above code
in them method »main«, except that »getNext« was replaced by
»next«:

public class Main
{
static class Counter
{ int value;
void reset(){ this.value = 0; }
void increment(){ if( value >= ++value )
throw new java.lang.RuntimeException(); }
public final java.lang.String toString()
{ return java.lang.String.valueOf( value ); }}

static class Integer
{ int value;
public Integer( final int value ){ this.value = value; }
public boolean isGreaterThan( final int value )
{ return this.value > value; }}

static final Counter counter = new Counter();

static final java.util.ArrayList<Integer> list =
new java.util.ArrayList<Integer>();

static
{ list.add( new Integer( 1 ));
list.add( new Integer( 11 ));
list.add( new Integer( 11 ));

java.lang.Runtime.getRuntime().addShutdownHook
( new java.lang.Thread
( new java.lang.Runnable()
{ public void run()
{ java.lang.System.out.println( counter ); }})); }

static final java.util.Iterator<Integer> integers = list.iterator();

public static void main( final java.lang.String[] args )
{
for( counter.reset(); integers.hasNext(); )
if( integers.next().isGreaterThan( 9 ))counter.increment(); }}

It prints »2« because in the list, there are 2 numbers
greater than 9. Thus, it has counted the numbers greater
than 9.

 

[Stefan Ram]

static class Counter
{ int value;
void reset(){ this.value = 0; }
void increment(){ if( value >= ++value )
throw new java.lang.RuntimeException(); }
public final java.lang.String toString()
{ return java.lang.String.valueOf( value ); }}

I say that a class has a »perfect type« encapsulation«, when
one can change types used in the class so as to enhance it,
while its interface does not change.

The above Counter class has a perfect encapsulation of the
type of »value«. This means, to change it, say, from »int«
to »long« or to »double«, one has to change the one
occurence of »int« to »long« or to »double«, respectively,
and the whole program will immediately work correct again -
while the counter indeed will be enhanced, i.e., be able to
count to larger values.

 

[markspace]

Is there a way where I can compare C++ code to Java code?

I have to agree with Martin here. Do you understand C++? Do you
understand the C++ code you were given? Do you understand Java?

It seems to me that answering "yes" to all three would be a prerequisite
to completing your project. At least one of those answers seems like it
must be "no" at this point.

 

[DeAndrea Monroe]

  The above Counter class has a perfect encapsulation of the

  type of »value«. This means, to change it, say, from »int«
  to »long« or to »double«, one has to change the one
  occurence of »int« to »long« or to »double«, respectively,
  and the whole program will immediately work correct again -
  while the counter indeed will be enhanced, i.e., be able to
  count to larger values.

I think I asked the wrong question. I'm trying to do a loop that takes
a number, longer than one digit, as a whole. For example, I have a
case statement that goes up to the number 9 but if the number is 273,
it will only see the number 2 and ignore the 7 and 3. How would I do
about writing that loop?

 

[DeAndrea Monroe]

I have to agree with Martin here.  Do you understand C++?  Do you
understand the C++ code you were given?  Do you understand Java?

It seems to me that answering "yes" to all three would be a prerequisite
to completing your project.  At least one of those answers seems like it
must be "no" at this point.

I don't understand C++. I haven't taken any courses on it but I do
understand pieces of it. I partially understand Java, I took a course
like 3 years ago and I'm being reintroduced to it but I have forgotten
a few things.

 

[Stefan Ram]

I think I asked the wrong question.

Yes, I guessed so right from the start. That was the reason
to include the quotation about the English language / mother
language.

I'm trying to do a loop that takes a number, longer than one
digit, as a whole. For example, I have a case statement that
goes up to the number 9 but if the number is 273, it will
only see the number 2 and ignore the 7 and 3. How would I do
about writing that loop?

Well, this can not be answered in some sentences.

Imagine, someone would ask: Hello, I have a person lying
here before me and need to exchange his liver, I have a
knife and a blanket, how can I do this?

The answer would be: Either you have undergone extensive
training to do this, then you do not need to ask here, or,
otherwise, anything one could tell you via this
communication channel is of no use to you.

You need a more holistic and more humble approach. You can
not learn the above in isolation. You need to improve your
overall language skills. To do this you need to read books
on the topic and/or visit classes but at a more
simple/fundamental level first than the one you attempt to
tackle now. You are attempting to write a simple so-called
»scanner«, and once you mastered the fundamentals, you can
read texts about scanner construction or study scanners
written by others.

Concentrate on a single language (like C++ or Java) first
for about 3 years. (Some people need more, some need less.)

See

»Teach Yourself Programming in Ten Years - Peter Norvig«

http://norvig.com/21-days.html

.
--

FWIW: I wrote this about how to implement a simple
calculator in Java. Your question appears as exercise #4 below.

(If answering to the following post, one should please not
quote all of it, but only a few lines one directly refers to.)

In order to interpret or translate an expression (term), it is
decomposed into lexical units (tokens, words), which then are
used by a parser to build symbols and a structured
representation of the input. This representation then might be
evaluated or translated into some other representation.

The syntactial structuring resembles the rules for the
construction of an expression, which often is given by so-
called "productions" of the EBNF (extended Backus-Nauer-Form)
and which sometimes are left-recursive.

When writing a parser, the left-recursive productions sometimes
are a worry to the author, because it is not obvious how to
avoid an infinite recursion. The solution is to rewrite them as
right-recursive productions.

The addition with a binary infix Operator, for example, is
left associative. However, it is simpler to analyze in a
right-associative manner. Therefore, one analyzes the source
using right-associative rules and then creates a result
using a left-associative interpretation.

A left-associative grammar might be, for example, as follows.

<numeral> ::= '2' | '4' | '5'.
<expression> ::= <numeral> | <expression> '+' <numeral>.
start symbol: <expression>.

To analyze this using a recursive descent parser, one
prefers to use the following grammar.

<numeral> ::= '2' | '4' | '5'.
<expression> ::= <numeral>[ '+' <expression> ].
start symbol: <expression>.

This can be written using iteration as follows.

<numeral> ::= '2' | '4' | '5'.
<expression> ::= <numeral>{ '+' <numeral> }.
start symbol: <expression>.

However, the product is created in the sense of the
first grammar. Example code follows.

class Scan
{ final static String source = "5+4+2)";
static int pos = 0;
static char get(){ return source.charAt( pos++ ); }}

class Parse
{
static int numeral(){ return Scan.get() - '0'; }

static int expression(){ int result = numeral();
while( '+' == Scan.get() )result += numeral();
return result; }}

public class Start
{ public static void main( final String[] args )
{ System.out.println( Parse.expression() ); }}

To be able to parse expressions with higher
priority, the grammar can be extended.

<numeral> ::= '2' | '4' | '5'.
<product> ::= <numeral> | <product> '*' <numeral>.
<sum> ::= <product> | <sum> '+' <product>.
start symbol: <sum>.

In iterative notation:

<numeral> ::= '2' | '4' | '5'.
<product> ::= <numeral>{ '*' <numeral> }.
<sum> ::= <product>{ '+' <product> }.
start symbol: <sum>.

In Java:

class Scan
{ final static String source = "5+4*2)";
static int pos = 0;
static char get( final boolean advance )
{ return source.charAt( advance ? pos++ : pos ); }}

class Parse
{
static int numeral(){ return Scan.get( true ) - '0'; }

static int product(){ int result = numeral();
while( '*' == Scan.get( false )){ Scan.get( true ); result *= numeral(); }
return result; }

static int sum(){ int result = product();
while( '+' == Scan.get( true ))result += product();
return result; }}

public class Start
{ public static void main( final String[] args )
{ System.out.println( Parse.sum() ); }}

Exercises

- What is the output of the above programs?

- Extend the last grammar and the last program so as
to handle subtraction.

- Extend the result of the last exercise in order
to handle division.

- Extend the result of the last exercise so that also
numbers with multiple digits are accepted.

- Extend the result of the last exercise so that also
terms in parentheses are accepted. The input "(2+4)*5)"
should give the result "30".

- Extend the result of the last exercise so that
also a unary minus "-" is recognized.

- Extend the result of the last exercise so that
more operators and functions are recognized.

- Extend the result of the last exercise so that
meaningful error messages are created for all
inputs that do not fulfill the rules of the input
language.

- Extend the result of the last exercise so that the
error messages also show the location where the error
was detected. It should be possible to enter an expression
that spans multiple lines, and an error message should
contain the number of the line where the error was
detected.

See also:

JEP - Java Mathematical Expression Parser
http://www.singularsys.com/jep/

Steven Metsker: Building Parsers with Java.
Addison-Wesley 2001, ISBN 0201719622.

A.W. Appel: Modern Compiler Implementation in Java.
Cambridge University Press 1998, ISBN 0521586542.

Implementing a scripting engine
http://www.flipcode.com/articles/scripting_issue01.shtml

http://compilers.iecc.com/crenshaw/

http://www.threedee.com/jcm/psystem/p2.zip

 

[DeAndrea Monroe]

  You need a more holistic and more humble approach. You can

  not learn the above in isolation. You need to improve your
  overall language skills. To do this you need to read books
  on the topic and/or visit classes but at a more
  simple/fundamental level first than the one you attempt to
  tackle now. You are attempting to write a simple so-called
  »scanner«, and once you mastered the fundamentals, you can
  read texts about scanner construction or study scanners
  written by others.

I apologize if I seem hostile, that is not my intent. I just feel like
I get mixed messages, some say be agressive and ask what questions
you're having. At the same time, I'm a little frustrated becaue I have
been working on this program for like 6 days and I'm still getting
errors. I don't understand why they are happening or how to fix them
directly.

 

[DeAndrea Monroe]

I have reposted my revised code. I'm getting the errors:

<identifier> expected
cannot find symbol
missing return statement
incompatible types
'{' expected

 

[markspace]

I don't understand C++. I haven't taken any courses on it but I do
understand pieces of it. I partially understand Java, I took a course
like 3 years ago and I'm being reintroduced to it but I have forgotten
a few things.

OK, it's good to know where we are at then. I think the first step is
to understand the C++ program. Could you check that in so we can take a
look at it? I didn't see it on the Google code site where you linked to
in your first post.

 

[DeAndrea Monroe]

OK, it's good to know where we are at then.  I think the first step is
to understand the C++ program.  Could you check that in so we can take a
look at it?  I didn't see it on the Google code site where you linked to
in your first post.

It's a handout that was given to me from an instructor.

 

[markspace]

I have reposted my revised code. I'm getting the errors:

<identifier> expected
cannot find symbol
missing return statement
incompatible types
'{' expected

The first of these that I see occurs on line 111. First, when you give
us errors, it's good to give the whole error message, so that we can see
what it is you are really doing.

Second, that line 111 is:

while ((!Operator.isEmpty(); evaluate <= Operator.stackTop())

A. We don't have access to the Operator source file, so there's no way
to tell if it is correct.

B. Regardless, the while() statement does not take a ; in its condition
statement. That's just a syntax error plain and simple.

You really need to go to your computer lab and hang out there. These
are questions that absolutely must be take up with your instructor. If
you don't have access to a computer lab or your instructor off hours,
then I'd suggest a different school, as you are wasting time and money
at the current one.