Chapter 4

1
Chapter 4 Operators

• Wayne Machuca
• Mt Hood Community College

2
Overview

• The Assignment Operator
• String Operator\
• Comparison Operators
• Logical Operators

3
The Assignment Operator

• In most computer languages, variables are
  assigned in a process called assignment
• Variable Expression
• Example firstName Herman
• The value Herman is assigned to a space in
  memory identified as firstName

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04_01.pl
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Multiple Assignment

• Perl has an interesting capability of assigning a
  single value to multiple variables at the same
  time.
• It is different in that each variable is
  identified and valued at the same time
• The assignment still goes right to left

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04-02.pl
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Arithmetic Operators

• Perl has a familiar list of operators
• addition
• - subtraction
• multiplication
• / division
• modulus division
• exponentation

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Modulus

• Remember long division? Modulus is used in a
  division to return the remainder. 33 / 7 4
  remainder 5
• Example remainder 33 7 remainder
  will equal 5

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Exponentiation

• Exponentiation means to raise a value to the
  power of
• You have seen 53 125
• In Perl you write exponent 5 3
  exponent will equal 125

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04-03.pl

• Always document your programs the same way

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04-03.pl

• Identify distinct sections of code

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04-03.pl

• Document what the code is doing

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Other Operators

• Perl supports incrementer (increase) and
  decrementer (decrease) operators
• Makes the code look more efficient
• Effective in working with increasing and
  decreasing counters

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Other Operators

• Examplescnt is the same as cnt cnt
  1cnt-- is the same as cnt cnt
  1cnt5 is the same as cnt cnt
  5cnt-5 is the same as cnt cnt -
  5cnt5 is the same as cnt cnt
  5cnt5 is the same as cnt cnt
  5cnt/5 is the same as cnt cnt / 5

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You are going to love this

• You can place the incrementer either before or
  after the variable name
• You will get different resultscntis not
  the same ascnt

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Watch
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Basic Looping

• We will use the while statement to discuss
  looping from the context of using a counter.
• We will cover looping structures in depth later.

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Looping with a counter
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String Operators

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

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Variable Interpolation

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

Perl will try to resolve the variablesomethingab
le
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Bad Fix

• Add a space to identify comfort, but

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Interesting Perl Fix
Include Curly Braces
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Substrings

• Perl allows you to extract parts of a
  stringsubstr(stringb, startpos, length)

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Substring
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Changing Case

• You have several commands to allow you to change
  the case of a string
• uc Convert to upper case
• lc -- Convert to lower case
• ucfirst Convert the first char to upper
• lcfirst Convert the first char to lower

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Changing case Something strange
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Combining Strings and Number

• Rule 1 DontRule 2 But if you do, be careful

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This is strange but it works
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This fails
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Use the dot to concatenate
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Comparison Operators

• To test numeric scalar values, use the following
  comparison operators
• gt (greater than)
• (equal to)
• lt (less than)
• gt (greater than or equal to)
• lt (less than or equal to)
• ! (not equal to)

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Watch the comparison on a simple conditional test
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String Comparisons are Different
Wrong
34
This is better
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String comparison operators

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

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Logical Operators

• Use to evaluate whether a condition is true or
  false
• Testing the Boolean state of a condition

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Lets try one
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Done
39
Lab 3

• Add to Lab 3 the following
• If the customer did not order any quantity of an
  item, do not print that item on the invoice
• Keep the item number accurate for the individual
  order (3 items should be listed as 1,2 and 3)

40
Lab 3

• Charge sales tax based on the customers address.
• OR 0, CA 7.25, WA 8
• Add salesTax and grandTotal amounts to the
  invoice
• Display a message at the end of the program
  identifying the item that sold the greatest
  poundage.
• Product (name) sold the most with (number) of
  pounds

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Lab 3

• State names must be all caps.