CSC207.01 2014S, Class 21: Exam 1 Discussion
============================================

_Overview_

* Preliminaries.
    * Admin.
    * Upcoming work.
    * Questions.
* Problem 1 - Testing.
* Problem 2 - Averaging.
* Problem 3 - Stringing.
* Problem 4 - Replacing.
* Additional issues.
* Makeup.

Preliminaries
-------------

### Admin

* Exam 1 will be returned at the end of class.
* MathLAN may or may not be acting up again.  But we have no lab today,
  so it's okay.
* Our graders are working hard, but they've discovered just how much time
  it takes to grade well.
* Extra credit: 
    * Town hall meeting Tuesday at noon in JRC 101 or 7:30pm in Harris.
    * Wellness fair.
    * CS Extras: The new CS Curriculum.
    * More?

### Upcoming work.

* Reading for Tuesday: Anonymous inner classes.
* Homework 5 is due *next* Wednesday (March 5), but you may need two
  weeks to get it done.
* Makeup for exam 1 is due Sunday night.

### Questions on the homework?

Problem 1 - Testing
-------------------

Normal cases

* A bunch of identical positive numbers
* A bunch of different positive numbers
* Mixed positive and negative numbers
    * Negative result
    * Positive result
    * Zero result
* A bunch of identical negative numbers
* A bunch of different negative numbers
* Small arrays and big arrays 
    * Really big arrays
  
Particular tests that we found useful

* [1,-2,3,-4,5,-6]
* [1,2,3,4,5]
* [-2,1]

Special cases

* Rounding 
    * test(1/2, average([0,1]))
    * test(3/2, average([1,2]))
    * Down for positive, up for negative
    * Using a variety of fractional portions

Edge cases

* Mixing things near Long.MAX_VALUE and Long.MIN_VALUE
* *Near* Long.MAX_VALUE and *Near* Long.MIN_VALUE
* A really really really big array (say more than Integer.MAX_VALUE elements,
  all of them near Long.MAX_VALUE)
* Does it throw exceptions
    * (Beyond scope of what I expected.)

Problem 2 - Averaging
---------------------

* Using doubles.

Problem 3: Stringify
--------------------

* It might have been helpful to write a helper that does the conversion
  in memory, before writing to the file.

* What do you see as the difference between

         String line = infile.readLine();
         while (line != null)
           {
             ...
             line = infile.readLine();
           } // while

  and

         String line;
         while ((line = infile.readLine()) != null)
           {
             ...
           } // while

* What do you see as the difference between

         ch = line.charAt(i);
         if (ch == '\t')
           ...
         else if (ch == '\n')
           ...
         else if (ch == '\\')
           ...
         else if (ch == '\"')
           ...
         else
           ...

  and

         switch (ch = line.charAt(i))
           {
             case '\t':
               ...;
               break;
             case '\n':
               ...;
               break;
             case '\\':
               ...;
               break;
             case '\"';
               ...;
               break;
             default:
               ...;
               break;
           } // switch

Why did you write `"\\" + "n"` rather than `"\\n"`?

* Computers are evil and failed to work appropriately for the second.

Problem 4 - Replacing
---------------------

* Some of you used `String.replace`.  I thought the problem was pretty
  clear that that approach was not permitted.
* Everyone who did a real solution should have written a helper method
  that checked whether the string matched at the given position.
* Most of you used (approximately)

        int i = 0;
        while (i < contents.size-pattern.length())
          {
            if (this.matchesAt(i, pattern))
              {
                this.remove(i, i + pattern.length());
                this.prepend(i, replacement);
                i += pattern.length();
              } // if match at position i
            else // if no match at position if
              {
                i++;
              } // if no match at position i
          } // while

* This solution is potentially quadratic in the size of the input
  (e.g., `"aaaaaa".replace("a","b")`)

Other Issues
------------

* Formatting
* Tarballs
* Sam's errors


Makeup
------

Although I said that I was not going to allow a makeup exam, there were
enough problems on problems 2 and 4 that I will allow you to make those
problems up for partial credit.