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Chapter 4 – Operators

Wayne MachucaMt Hood Community

College

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OverviewOverview

The Assignment OperatorThe Assignment Operator

String Operator\String Operator\

Comparison OperatorsComparison Operators

Logical OperatorsLogical Operators

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The Assignment OperatorThe Assignment Operator

In most computer languages, variables are In most computer languages, variables are assigned in a process called assigned in a process called assignmentassignment

Variable = ExpressionVariable = Expression

ExampleExample$firstName = “Herman”;$firstName = “Herman”;

The value “Herman” is assigned to a The value “Herman” is assigned to a space in memory identified as $firstNamespace in memory identified as $firstName

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04_01.pl04_01.pl

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Multiple AssignmentMultiple Assignment

Perl has an interesting capability of Perl has an interesting capability of assigning a single value to multiple assigning a single value to multiple variables at the same time.variables at the same time.

It is different in that each variable is It is different in that each variable is identified and valued at the same timeidentified and valued at the same time

The assignment still goes right to leftThe assignment still goes right to left

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04-02.pl04-02.pl

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Arithmetic OperatorsArithmetic Operators

Perl has a familiar list of operatorsPerl has a familiar list of operators + addition+ addition - subtraction- subtraction * multiplication* multiplication / division/ division % modulus division% modulus division ** exponentation** exponentation

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Modulus %Modulus %

Remember long division? Remember long division? Modulus is used in a division to return the Modulus is used in a division to return the remainder.remainder.

33 / 7 = 4 remainder 533 / 7 = 4 remainder 5

ExampleExample $remainder = 33 % 7; $remainder = 33 % 7; $remainder will equal 5 $remainder will equal 5

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ExponentiationExponentiation

Exponentiation means to raise a value to Exponentiation means to raise a value to the power ofthe power of

You have seen 5You have seen 533 = 125 = 125

In Perl you writeIn Perl you write$exponent = 5 ** 3;$exponent = 5 ** 3;

$exponent will equal 125 $exponent will equal 125

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04-03.pl04-03.pl

Always document your programs the same Always document your programs the same wayway

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04-03.pl04-03.pl

Identify distinct sections of codeIdentify distinct sections of code

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04-03.pl04-03.pl

Document what the code is doingDocument what the code is doing

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Other OperatorsOther Operators

Perl supports incrementer (increase) and Perl supports incrementer (increase) and decrementer (decrease) operatorsdecrementer (decrease) operators

Makes the code look more efficientMakes the code look more efficient

Effective in working with increasing and Effective in working with increasing and decreasing countersdecreasing counters

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Other OperatorsOther Operators

ExamplesExamples$cnt++; is the same as $cnt = $cnt + 1;$cnt++; is the same as $cnt = $cnt + 1;$cnt--; is the same as $cnt = $cnt – 1;$cnt--; is the same as $cnt = $cnt – 1;

$cnt+=5; is the same as $cnt = $cnt + 5;$cnt+=5; is the same as $cnt = $cnt + 5;$cnt-=5; is the same as $cnt = $cnt - 5;$cnt-=5; is the same as $cnt = $cnt - 5;$cnt%=5 is the same as $cnt = $cnt % 5;$cnt%=5 is the same as $cnt = $cnt % 5;$cnt*=5 is the same as $cnt = $cnt * 5;$cnt*=5 is the same as $cnt = $cnt * 5;$cnt/=5 is the same as $cnt = $cnt / 5;$cnt/=5 is the same as $cnt = $cnt / 5;

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You are going to love thisYou are going to love this

You can place the incrementer either You can place the incrementer either before or after the variable namebefore or after the variable name

You will get different resultsYou will get different results

++$cnt;++$cnt;is not the same asis not the same as$cnt++;$cnt++;

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WatchWatch

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Basic LoopingBasic Looping

We will use the while statement to discuss We will use the while statement to discuss looping from the context of using a looping from the context of using a counter.counter.

We will cover looping structures in depth We will cover looping structures in depth later.later.

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Looping with a counterLooping with a counter

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String OperatorsString Operators

The Concatenator OperatorThe Concatenator Operator Use the dot (.) to join stringsUse the dot (.) to join strings

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Variable InterpolationVariable Interpolation

““If a variable is contained in a string If a variable is contained in a string enclosed in double quotes, the variable is enclosed in double quotes, the variable is replaced by the value of the variable.”replaced by the value of the variable.”

Perl will try to resolve the variable$somethingable

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Bad FixBad Fix

Add a space to identify $comfort, but…Add a space to identify $comfort, but…

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Interesting Perl FixInteresting Perl FixInclude Curly Braces

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SubstringsSubstrings

Perl allows you to extract parts of a stringPerl allows you to extract parts of a string

substr(stringb, startpos, length)substr(stringb, startpos, length)

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SubstringSubstring

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Changing CaseChanging Case

You have several commands to allow you You have several commands to allow you to change the case of a stringto change the case of a string uc – Convert to upper caseuc – Convert to upper case lc -- Convert to lower caselc -- Convert to lower case ucfirst – Convert the first char to upperucfirst – Convert the first char to upper lcfirst – Convert the first char to lowerlcfirst – Convert the first char to lower

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Changing case – Something strangeChanging case – Something strange

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Combining Strings and NumberCombining Strings and Number

Rule #1: Don’tRule #1: Don’tRule #2: But if you do, be carefulRule #2: But if you do, be careful

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This is strange but it worksThis is strange but it works

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This failsThis fails

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Use the dot to concatenateUse the dot to concatenate

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Comparison OperatorsComparison Operators

To test numeric scalar values, use the To test numeric scalar values, use the following comparison operatorsfollowing comparison operators > (greater than)> (greater than) = = (equal to)= = (equal to) < (less than)< (less than) >= (greater than or equal to)>= (greater than or equal to) <= (less than or equal to)<= (less than or equal to) != (not equal to)!= (not equal to)

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Watch the comparison on a simple Watch the comparison on a simple conditional testconditional test

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String Comparisons are DifferentString Comparisons are Different

Wrong

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This is betterThis is better

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String comparison operatorsString comparison operators

Use these for stringsUse these for strings eq eq ne ne lt lt gt gt le le ge ge

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Logical OperatorsLogical Operators

Use to evaluate whether a condition is true Use to evaluate whether a condition is true or falseor false

Testing the Boolean state of a conditionTesting the Boolean state of a condition

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Let’s try one…Let’s try one…

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DoneDone

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Lab 3 Lab 3

Add to Lab 3 the following:Add to Lab 3 the following:

If the customer did not order any quantity If the customer did not order any quantity of an item, do not print that item on the of an item, do not print that item on the invoiceinvoice

Keep the item number accurate for the Keep the item number accurate for the individual order (3 items should be listed individual order (3 items should be listed as 1,2 and 3)as 1,2 and 3)

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Lab 3Lab 3

Charge sales tax based on the customer’s Charge sales tax based on the customer’s address.address. OR = 0%, CA = 7.25%, WA = 8%OR = 0%, CA = 7.25%, WA = 8%

Add salesTax and grandTotal amounts to the Add salesTax and grandTotal amounts to the invoiceinvoice

Display a message at the end of the program Display a message at the end of the program identifying the item that sold the greatest identifying the item that sold the greatest poundage.poundage. ““Product (name) sold the most with (number) of Product (name) sold the most with (number) of

pounds”pounds”

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Lab 3 Lab 3

State names must be all caps.State names must be all caps.