LECTURE 17: February 11, 2008

Quiz: WEDNESDAY (Up to lecture 11)
HW1 graded
HW2 solutions coming soon
Today: Q&A

The Quiz will be for the whole class period. 

#s refer to Sample Quiz questions:

#6 The computer recognizes $Str= Ò Ò; as something false, as in : if ($Str) {... what is in the
round brackets would be false.

#9 Let's program it with a while loop this time:
        Prime with ÒwhileÓ

        $Num=<>
        chomp $Num;
        $IsPrime=1;
        $Count=2;
        
        while ($Count<$Num) {
                if  (($Num%$Count)==0) {
                        $IsPrime=0;
                }
        } $Count++;
        if...

for (A ;B; C) {
A
while (B) {...
C
}

We also could do for #9:

$Num=<>; chomp $Num;
$HasADivisor=0;
for($Count=2;$Count<$Num; $Count++) {
        if (($Num % $Count)==0) {
                $HasADivisor=1;
                }
        }
Might see a question on the quiz regarding nested loops.





Array problems:

If we do:

%H=(1,3,10,12,8,10);
print %H;
-> 131012810  (can't tell one thing from the other)
@A=%H;
print @A;
->131012810 (still same thing)
print Ò@AÓ;
1 3 10 12 8 10 (now it is readable)
print Ò%HÓ;
-> %H 

Union of two arrays:
* @A1, @A2 are arrays
* Produce @A3 with elements that are in @A1 and @A2
*Not just adding the two arrays together as (@A1, @A2); But need to actually check for duplicates.

        @A1=(ted, ann,bill);
        @A2=(ann, george, frank, dean)
        ->@A3= (ted, ann, bill, george, frank, dean);
        
        
        Start with @A3=@A1
        Loop through elements of @A2
                -check if already in @A1
                -If not, add to @A3

        Perl for Union:

        @A3=@A1;
        Foreach $Val (@A2) {
                $Count=0;
                Foreach $Val2 (@A1) {
                if ($Val eq $Val2) {
                        $Count++;
                        
                        }
                }
                if ($Count==0){
                push @A3, $Val
                }
        }