my $number = 10;
while ($number > 0) {
Do something with the $number;
$number = $number - 1;
}
What is the first number that we do something
with? What is the last number? Hint: replace
do something
with a line that prints the number. Then run the small program that results.
QIP.2. Change the program you wrote in question 1 to count up instead of down.
QIP.3. The DiceRoll.pl program contains a comment:
followed by the random_integer routine that the comment mentions.# random_integer($low, $high) returns a random integer between $low and $high # inclusive. # Assumption: $low < $high, and both are integers.
sub random_integer {
my ($low, $high) = @_;
my $range = $high - $low + 1;
my $random_fraction_of_range = rand($range);
return $low + int($random_fraction_of_range);
}
Such comments are often useful when you're trying to modify a program --
they tell you what a section of the program does, so that you don't have
to decipher it line by line.
On the other hand, comments aren't always truthful -- perhaps the author was mistaken, or perhaps the program was modified but the comment wasn't. So we sometimes need to test the truth of a comment.
Write a program that will test random_integer -- something that will increase (or utterly destroy) your confidence that the line
will always set $die_value to an integer between 1 and 6 - never 0 or -23 or 1024 or 3.14159.my $die_value = random_integer(1,6);
This program doesn't need to be elaborate -- perhaps it will simply print out ten trials of random_integer.
For your convenience, click on random_integer.pl for a file with the random_integer section of the code already typed in.
QIP.4. If you have programming experience you might enjoy writing a more elaborate test program - you could automatically check 10 million trials of random_integer. That's not the exercise, though.
The exercise is to answer these questions:
Assume that random_integer passes the 10-trial test. Your confidence in the comment will increase somewhat. Then you run the 10-million-trial test. If random_integer passes this test, will your confidence increase a million times as much? Why or why not?QIP.5. The comment says:
In other words, the author doesn't guarantee that random_integer($low, $high) will return a random integer between $low and $high inclusive unless $low is less than $high and both are integers. Is this too conservative? What happens if $low or $high are not integers? If $low equals $high? If $low is less than $high?# Assumption: $low < $high, and both are integers
QIP.6. Take out int in the last line of random_integer, so that it looks like this:
sub random_integer {
my ($low, $high) = @_;
my $range = $high - $low + 1;
my $random_fraction_of_range = rand($range);
return $low + $random_fraction_of_range;
}
Run your 10-trial test. What does int do?
QIP.7. Now take out rand in the next to last line:
sub random_integer {
my ($low, $high) = @_;
my $range = $high - $low + 1;
my $random_fraction_of_range = $range;
return $low + $random_fraction_of_range;
}
What does rand do?
QIP.8. By fooling around with some working program, determine when upper case/lower case makes a difference in the operation or results of a Perl program.