Alright, exercise 4 has been graded. Not too many problems with the code
but there were some consistent mistakes being made that should be pointed
out.

Syntax - many of you were forgetting semi-colons at the end of lines. It
is alright to declare and initialize multiple variables on one line. This
will compile. However, it is bad style to do this. While you may declare
multiple variables on one line, it is generally a good practice to
initialize only one per line.

Comments, comments, comments. Many papers had none. The comments which
were found on the page were written by Kiri to explain what you needed
to do. These were not there to comment the code which you wrote in. If
the exercise had received a grade for style, 90% of the class would have
gotten a zero.

For loops. Obviously, these were the heart of exercise 4. And for those
of you who continue in CS, for loops will follow you through Object
Oriented Programming. Here are some basic pointers:

for (init; cond; incr)
{
  /*body*/
}

Here's something neat that no one knew about. You can use the empty
statement in place of any of these.
so, the code:

for (int i = 0; i <= 10; i++)

is the same as:

int i = 0;
for (; i <= 10; i++);

therefore, if you have i already initialized before the for loop, you
don't need to reinitialize it in the init statement. Just leave it
empty :)

You can do this for conditions, too.

for (int i = 0; ; i++) {}

is an infinite loop that will continue to increment i, and will only
terminate if there is a break; or System.exit(); in the loop.

for (int i = 0; i <= 10;) {}

is an infinite loop that will keep i at 0 and will only break if the
above commands are in the loop, or if i is set to a value >10 in the
loop.

Once you have the for loop down, you must also straighten out what
values go where. Several of you mixed up the conditions, so make sure
what you are putting in the loop makes sense. One example was:

num = Savitch.readLineInt();

for (int num = 1; num != 0; num--)
As you can see if you examine this carefully, the data stored in num
is replaced with 1, and the loop only runs once, instead of the
number that the user specified. Be careful with your loop conditions,
or later on you will be getting very strange (and often hard to find)
errors while running your programs with loops. :o

Lastly, in calculating the percentage - chances were very likely that
you would end up with a decimal value. In addition, remember the
precedence that Kiri talked about in lecture.

heads / num_flips * 100 will always give 0 unless heads == num_flips

Therefore, you needed to fix this in the following way:

heads / ((double) num_flips) * 100

this would give the correct value for percentage. Notice that the
cast is performed first, and then when the div is performed, it uses
float and not integer division. It was alright if you left out the
100, that was a matter of personal taste.

As always, if you have questions, please see me during office hours,
and I will be more than happy to go over anything from the course,
as well as anything outside of the course, with you.

- b