**********************
SEE EXPRESSION VALUES - DONE
**********************
last modified: 12-12-11

Enter a C++ expression in a textfield, click a button, and see its
value. (If the C++ expression is not syntactically legal, the
value given should simply be "Bad expression".)

STATUS: DONE
FIRST PASSED: quite a bit before 11-01-11; didn't think to
              record this until later. This was the second
              user story completed.
acceptance tests last attempted: 12-12-11
acceptance tests last passed:    12-12-11 
                                 (but with odd-not-fatal Mac/Linux
				 behavior on 0/0)

-------------------
acceptance test 1
-------------------
int expression works?

(if necessary:
1. run:
   python3 theGui.pyw
)

2. enter 
3 + 5
   ...into expression textfield
3. click Execute button
4. See if 8 appears in result text area.

LAST TESTED: 12-12-11
LAST PASSED: 12-12-11

             comment: why do I get the following error messages in
	     the Terminal from which I called python3?:

[12-12-11 - still getting messages such as the following]
Nov 10 15:27:12 Math-Tuttle-OSX.local Python[73788] <Error>: kCGErrorInvalidConnection: CGSGetWindowTags: Invalid connection
Nov 10 15:27:12 Math-Tuttle-OSX.local Python[73788] <Error>: kCGErrorFailure: Set a breakpoint @ CGErrorBreakpoint() to catch errors as they are logged.

-------------------
acceptance test 2
-------------------
double expression works?

1. enter 
1.0 / 3.0
   ...into expression textfield
2. click Execute button
3. See if (approximately) 0.333333 appears in result text area.

LAST TESTED: 12-12-11
LAST PASSED: 12-12-11

[no longer noting these odd messages -- basically,
they are always happening when I interact with the windows...]

-------------------
acceptance test 3
-------------------
bool expression works?

1. enter 
(1 < 3) && (3 < 5)
   ...into expression textfield
2. click Execute button
3. See if true appears in result text area.

LAST TESTED: 12-12-11
LAST PASSED: 12-12-11

-------------------
acceptance test 4
-------------------
expression with a math library function works?

1. enter 
sqrt(2) + ceil(sqrt(3))
   ...into expression textfield
2. click Execute button
3. See if (approximately) 3.41421 appears in result text area.

LAST TESTED: 12-12-11
LAST PASSED: 12-12-11

-------------------
acceptance test 5
-------------------
expression with a syntactically "bad" function gives the
value "Bad expression"?

1. enter 
sqrt 2 + 3
   ...into expression textfield
2. click Execute button
3. See if "Bad expression" appears in result text area.

LAST TESTED: 12-12-11
LAST PASSED: 12-12-11

-------------------
OPTIONAL acceptance test 6
-------------------
expression that, strictly speaking, compiles, but causes
a run time error when run results in an error message

1. enter 
0 / 0
   ...into expression textfield
2. click Execute button
3. See if an appropriate error message appears in result text area.

12-12-11 - no; get a value, 1690618312
           Mr. Taijala notes that is "expected" behavior for
           this on Mac and maybe Linux (!); error message
	   is just on Windows;

4. Check "Compile strictly", then again click "Execute".
5. This should now not compile? 
   12-12-11: Now get "Bad expression", nice;

6. Check "Detailed error messages", then again click
   "Execute".
7. This should still not compile? But with compiler messages?
   12-12-11: Now get the appropriate compiler
   warning-that-is-the-desired-error-message (division by 0);
   nice!

*   close the Helper++ window to close program

LAST TESTED: 12-12-11
LAST PASSED: maybe 12-12-11, if don't consider "expected" 
             Mac/Linux behavior here a bug;