Announcements:

HW1 graded Monday
HW2 due next Wednesday (late by Friday)
Hard copies of HW2 available now
Quiz on Feb. 13th (tentatively)


Today:

Lists (Arrays)
sort
"return valves"
foreach
examples
indexing


@A = (1,2,7,3,-1,9)
@A2 = reverse @A
	A2 is (9,-1,3,7,2,1)
	A is still (1,2,7,3,-1,9), thus reverse does NOT change A.


Sorting arrays:

@A = ("abc" , "xyz" , "ged");
@A2 = sort @A; [sorts in ASCll-betical order]
@A2 is ("abc" , "ged" , "xyz") [A is still unchanged]
@A3 = (3,1,6,7,10);
@A4 = sort @A3;
@A3 is still the same
@A4 is (1,10,3,6,7) [does NOT treat string as numbers]

To sort numerically:

@A5 = sort {$a <=> $b} @A3; [this will sort numerically in ascending order]
@A5 is (1,3,6,7,10)
@A6 = sort {$b <=> $a} @A3; [this will sort numerically in descending order]
@A6 is (10,7,6,3,1)
@A7 = sort {$a cmp $b} @A; [same as sort @A]
@A7 is ("abc" , "xyz" , "ged")
@A8 = sort {$b cmp $a} @A; [sorts text in descending order]
@A8 is ("xyz" , "ged" ,  "abc")
Don't try : sort {$a > $b} @A3 [will not do wht you want it to do]




Example:

User enter strings until they enter "q". Print out a sorted list of strings.

Solution:

$Str = "";
@List = ();
while ($Str ne "q") {
	print 'Enter a string or "q": ';
	$Str = <>
	chomp $Str;

	if ($Str ne "q") {
		push @List,$Str;
	}
}
@List = sort @List;
print "@List\n";


Looping through an array:

@A = ("abc" , "xyz" , "ged")
foreach $Var (@A) {
}					[will go through each one of the values in the list]

Example:

Print elements of array on separate lines.

Solution:

$Str = "";
@List = ();
while ($Str ne "q") {
	print 'Enter a string or "q": ';
	$Str = <>
	chomp $Str;

	if ($Str ne "q") {
		push @List,$Str;
	}
}
@List = sort @List;
foreach $Str (@List) {	
	print "$Str\n";
}
Example: Find largest number in an array (using foreach).

Solution:

@A = (....);
$Big = -1000000;
Foreach $Num(@A) {
	if ($Num > $Big) {
		$Big = $Num;
	}
}
print "$Big\n";


Example: Given an array of strings @A, and a string $Str, is $Str in @A?

Solution:

Foreach $Str2 (@A) {
	if ($Str eq $Str2) {
		print "I\n";
	}
}