DAY 4: Control Structures

Vamshi Krishna .S

A statement block is a sequence of statements, enclosed in matching curly braces. It looks like this:

{ first_statement; second_statement; third_statement; ... last_statement; # last statement semicolon is optional. }

print "how old are you? "; $a = <STDIN>; chomp($a); if ($a < 18) { print "So, you're not old enough to vote, eh?\n"; } else { print "Old enough! Cool! So go vote!\n"; $voter++; # count the voters for later }

print "how old are you? "; $a = <STDIN>; chomp($a); unless ($a < 18) { print "Old enough! Cool! So go vote!\n"; $voter++;

Arrays are a special type of variable that store list style data types. Each object of the list is termed an element and elements can either be a string, a number, or any type of scalar data including another variable.

Array variables have the same format as scalar variables except that they are prefixed by an @ symbol.

Arrays can also hold arrays.

 array variable is a variable which is a list of scalars (ie numbers and strings). Array variables have the same format as scalar variables except that they are prefixed by an @ symbol.

@var = (value1..valueN);

@var = (“str1”,”str2”) ($a, $b) = @alphabets;

# $a and $b are the first two elements of @alphabets array

#!/usr/bin/perl

main(@ARGV); my $days =qw^Sun Mon

Tue Wed Thu Fri Sat^; Print @days; My $days=31; Print $days;

# It is valid to use the same name for scalars and array types.

My @array1 =(1,2,3); My @array2 = (@array1 ,4,5,6); Print “@array2”; # prints 1 2 3 4 5 6 Print $array2[2]; # prints 3

Print scalar @array2 # Here the scalar will contain the value 6 , as

the total no’of elements in the array2 is equal to 6

#!/usr/bin/perl

use warnings;use strict;say “input a number”;# functionality same as “print” , adds a new line character at the endMy chomp($choice =<STDIN>);

print qw(BMW Ferrari McLaren Jaguar )[$choice]);

OUTPUT:- McLaren

If you input a decimal value .. Choice = 1.2 then perl will round if off and will output Ferrari.

If you input a negative number.. Choice = -1 then perl starts counting backwards from the end of the list.

LIST Slices instead of putting a scalar value [$choice].. We can also

print out multiple values in the list by putting a list of index values

(20,30,99,15,22,13,56,76,34)[2,5,7] This can also be used on strings.

What happens when you assign a array to a scalar? @array1 = qw(a b c d); $scalar1 = @array1; Print “array cotents:” @array1 # prints with no spaces Print “array contents: @array1” # prints with spaces @array1 = (1,2,3,4,5) Print @array1 “\n”; Print “@array1\n” $scalar1 = “@array1\n”; is Same as $scalar = “1 2 3 4 5\n”; $scalar = @array1; is same as $scalar = 5 # as the total elements

in array is 5

(1 .. 10) ( -9 .. 9) (a .. z)

Cant mix up the list of elements list .. (a .. 5) or (-1 .. B) etc.,

Always the right-hand element should be higher than the left-handed element.

We can mix up the Slices and ranges.. For effective programming @coins = qw(Quarter Dime Nickel Penny); @slicecoins = @coins[0,2]; Say "@slicecoins"; # prints 0th index value “Quarter” and 2nd value “Nickel”

with Spaces b/w strings.

$a = (@array)[3];

My @array1= Print $array1[1]

@lang = qw(java python perl c); My $element;# declating scalar var for iteration For $element (@lang) { print $element “\n”; } For <iterator> (<list of array>) BLOCK If we don’t supply an iterator of our own.. Perl supplies a

special variable S_ which is often used in perl functins as default value

@array1 = (1,2,3,4); Print “before @array1 \n” For (@array1) {$_ * = 10} Print “after @array1\n”

#!/usr/bin/perl my @coins =

("Quarter","Dime","Nickel"); # ADD ELEMENTS push(@coins, "Penny"); print "@coins"; print "<br />"; unshift(@coins, "Dollar"); print "@coins";

# REMOVE ELEMENTS pop(@coins); print "@coins"; shift(@coins);

Adding elements is a breeze, we use the following functions to add/remove and elements:

push() - adds an element to the end of an array.

unshift() - adds an element to the beginning of an array.

pop() - removes the last element of an array.

shift() - removes the first element of an array.