CSc 398        Mid-Term Test               19 March 1999      Page 1

   >>>>>>>>>>>>>>>>>>>>>>>>>>ANSWERS<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
   1. (15 points)  Assume that T is an array of numbers.  Write three
      different code fragments, each using  a different collection method,
      to find the sum of the squares of the numbers in T.

   T:=0.
   S do:[:each| T:=T+each squared]

   T:=0.

   S with:S do:[:i :j|T:=i*j+T]
   S inject:0 into:[:tot :each| tot+each squared]

   2. (10 points)  Assume that T is an array of points.  Write code which
      returns the points in an array sorted by the squared Euclidean distance
      of the points from the origin. (The squared Euclidean distance of (x,y)
      from the origin is x*x + (y*y).  Thus, the squared Euclidean distance
      of (2,3) is 13, the squared Euclidean distance of (3,3) is 18, etc.)

     (T asSortedCollection sortBlock:[:a :b|
                 a x squared + a y squared < (b x squared + b y squared)])
             asArray

   3. (15 points)  Assume that T is an array with a variety of entries
      (e.g., strings, points, numbers, characters, etc.).  Let
      R:=ReadStream on:T and W:=WriteStream on:String new.  Write code such
      that after the code is executed, evaluating the expression "W contents"
      returns a string with (only) the numbers appearing in T.  For example,
      if T is #(a = 2 2@3 'hello' 44 (33)), then W contents would return
      '2 44'.

      R:=ReadStream on:T
      W:=WriteStream on:String new
      [R atEnd] whileFalse:[ (X:=R next) isNumber
                    ifTrue:[W nextPutAll:X printString,' ']].
      W contents

   4. (10 points) After the following code is finished executing, what is
    returned when the expression "T printString" is evaluated?

     T:=OrderedCollection new.
     X:=[1 to:20 by:3 do:[:each|T addLast:each. Processor yield]].
     Y:=[  11 to:17 do:[:i| T addLast:i. Processor yield]]
     X fork.
     Y fork

     'OrderedCollection(1 4 11 7 12 10 13 13 14 16 15 19 16 17 )'

   CSc 398        Mid-Term Test               19 March 1999      Page 2

   5. (50 points)  Write the description of a class Counter.  An instance of
     Counter can only count between some limits which are specified when
     the instance is instantiated.  (Such an object could provide protection
     against accessing arrays outside some given bounds.  Thus, if you have
     an array of size 10 and only accessed the array via an instance of
     Counter limited to 1, 2, ..., 10, then you could not go beyond the
     limits of the array.)  You should state the instance variable(s), and
     you should write the instance and class methods.

   "Test Example
17 March 1999"
Object subclass: #Counter
  instanceVariableNames:
    'bottom top count '
  classVariableNames: ''
  poolDictionaries: ''  !


!Counter class methods !
 
bottom:bottom top:top
  ^super new bottom:bottom top:top!
  
new
  ^self bottom:0 top:100! !



!Counter methods !
  
+inc
   (count+inc)>top | ((count+inc)<bottom)
    ifTrue:[self error:'Trying to increase aCounter out of range']
      ifFalse:[count:=count+inc]!
  
-dec
   (count-dec)>top | ((count-dec)<bottom)
       ifTrue:[self error:'Trying to decrement aCounter out of range']
      ifFalse:[count:=count-dec]!
  
bottom:bot top:tp
   bottom:=bot.
   top:=tp.
   count:=bottom!
  
count
   ^count!
   
dec
   count<=bottom
     ifTrue:[self error:'Trying to decrement aCounter below bottom']
     ifFalse:[count:=count - 1]!
   
inc
   count>=top
     ifTrue:[self error:'Trying to increment aCounter past top']
     ifFalse:[count:=count+1]!

reset
   count:=bottom! !