Name:
Directions: Work only on this sheet (on both sides, if needed); do not turn in any supplementary
sheets of paper. There is actually plenty of room for your answers, as long as you organize yourself
BEFORE starting writing.
Do not use any Python or Perl constructs which were not introduced either in lecture, discussion
section or our written materials.
1. (10) Give Python analogs of the following Perl items: shift @z,unshift @z,$x (prepends), $ARGV[3],
@z[9:12].
2. (15) Add code to kill() in our PLN program psax.py, which will display a confirmation query message, “Kill
this process (y,n)?”, on the line which is highlighted at the time the user hits the k key. The message will overwrite
the first part of that line. If the next key hit is not y, the function will simply return (the user can then hit u etc.
as a means of restoring the line); otherwise the original line will be restored and the process will be killed. In the
latter case, change the State column (16th character position in the line) to ‘K’. You are allowed to add a total of
nine lines maximum.
3. Consider a package RadixNum.pm whose objects will store nonnegative numbers in base-r form internally but
will present a scalar version of the numbers to the “outside world.” For example, consider this code (ignore the three
blank lines at the end for now):
use RadixNum;
tie $x,’RadixNum’,3,0; # base 3
tie $y,’RadixNum’,3,0; # base 3
$x = 5;
$y = $x + 20;
print $x,$y, "\n";
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________________________
________________________
This will print out 5 and 25, but internally $y, for instance, will also be associated with a reference to an anonymous
array (2,2,1), since the base-3 representation of 25 is 2·32+2·31+1·30. Note that the fancy name used for base
is radix, so in this example the radix is 3.
The object created by TIESCALAR() (not shown) is an anonymous hash which consists of an integer Radix, a
reference Digits to the anonymous array, and an integer Value containing the numeric value.
Part of the code in RadixNum.pm will be a subroutine torad(). It has as arguments the radix and value, and
returns a reference to the corresponding radix form of the value. For instance, the call torad(3,25) will return
\(2,2,1).
(a) (15) Fill in the blanks in torad():
sub torad {
my $rad = shift;
my $vl = shift;
my @ary = ();
if ($vl == 0) {@ary = (0);}
else {
while ($vl > 0) {
$t = $vl % $rad;
$vl = int($vl/$rad);
______________
}
}
return ______________;
}
(b) (15) An instance method printrad() will print out the radix form of the stored number. For instance, if $y is
storing 25, this function will print out 221. Fill in the blanks in the test code above (following the line printing
$x and $y), so that the radix form of $y is printed out, and the blanks in the function itself below. For full
credit, use no loops.
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