COMP111 : Quiz 8
Perl Programming
Hashes

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1) What is wrong? 

	#!/usr/local/bin/perl5 -w
	$bill{"Gates"} = "rich and famous";
	$bill{"Mr."} = "too excited";
	$bill{3} = 67;
	print "bill: $bill{"Gates"}\n";


Answer:  
Has double-quotes inside double-quotes in print statement. Should be:
	print "bill: ",$bill{"Gates"},"\n";


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2) What is the output? 

	#!/usr/local/bin/perl5 -w
	$bill{"Gates"} = "rich and famous";
	$bill{"Mr."} = "too excited";
	$bill{3} = 67;
	@a = (3,2,1);
	print "bill: $bill{@a}\n";


Answer:  
bill: 67

(@a is scalar context (array size) in $bill{@a}.)


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3) What is the output? 

	#!/usr/local/bin/perl5 -w
	$bill{"Gates"} = "rich and famous";
	$bill{"Mr. Bill"} = 1;
	@bill{1..4} = qw(very famous + nervous);
	@a = (3,4,2,1);
	print "bill: @bill{@a}\n";


Answer:  
bill: + nervous famous very



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4) What is the output? 

	#!/usr/local/bin/perl5 -w
	$bill{"Gates"} = "rich and famous";
	@bill{1..4} = qw(very famous + nervous);
	$bill{"Mr. Bill"} = 2;
	%bill = reverse %bill;
	@a = qw(very famous 2 nervous);
	print "bill: @bill{@a}\n";


Answer:  
bill: 1 2 Mr. Bill 4



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5) What is the output? 

#!/usr/local/bin/perl5 -w
$bill{"Gates"} = "rich and famous";
@bill{"Clinton","Mr."} = qw(very nervous);
@a = keys %bill;
print "bill: @bill{sort @a}\n";


Answer:  
bill: very rich and famous nervous


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6) What is the output? 

#!/usr/local/bin/perl5 -w
$bill{"Gates"} = "rich and famous";
@bill{"Clinton","Mr."} = qw(very nervous);
@bill{4..7} = qw(very famous + nervous);
@a = values %bill;
print "bill: $bill{keys %bill}\n";


Answer:  
bill: nervous

(Because keys %bill returns the size of the hash.)

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7) What is the output? 

#!/usr/local/bin/perl5 -w
$bill{"Gates"} = "famous";
@bill{"Clinton","Mr. Bill"} = qw(excitable excitable);
while(($k,$v) = each(%bill)){
	print "$k: $v\n";
}


Answer:  
Mr. Bill: excitable
Gates: famous
Clinton: excitable

(The order of the lines is random)


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8) What is the output? 

#!/usr/local/bin/perl5 -w
$bill{"Gates"} = "rich";
@bill{"Clinton","Mr."} = qw(very nervous);
@bob{qw(Bob Gates)} = qw(slow lazy);
@bill{keys %bob} = values %bob;
@a = sort keys %bill;
print "bill: @a\n";


Answer:  
bill: Bob Clinton Gates Mr.



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Regular Expressions

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1a) What regular expression would match
at least one x followed by zero or one y, followed by any 
number of z's?


Answer:  
	/x+y?z*/



1b) What is the simplest way to describe (in English) what 
is matched by the regular expression in 1a?


Answer:  
Matches anything with an "x"
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2a) What regular expression would match
any number of * followed by any number of backslashes?


Answer:  
	/\**\\*/



2b) What is the simplest way to describe (in English) 
what is matched by the regular expression in 2a?


Answer:  
Matches everything
(even matches empty string/blank line)
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3) What regular expression would match
any five characters, including newline?


Answer:  
/(.|\n)(.|\n)(.|\n)(.|\n)(.|\n)/
/(.|\n){5}/


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4) What regular expression would match
a line that contains "Bill" twice?
Examples:
BillBill
Bill Bill
BillGates Bill
ABillGatesBill Clinton


Answer:  
/Bill.*Bill/


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5) How would you write a subsitution the deletes all 
occurances of the string "Bill" in $_?

Answer:  
s/Bill//;