Internet Software Architectures

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Internet Software Architectures

• Lecture Two
• Operators and Flow Control

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Objectives

• By the end of this lecture the student should
• Understand how comparison operators work in PHP
• Understand how to control the flow of a PHP
  script
• Be able to apply the various PHP operators

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Environment Variables

• phpinfo() produces web page
• With environment and php variables displayed
• Accessible within php by name
• Eg REMOTE_ADDR returns IP address of client

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Comparison Operators

• ! ! lt gt gt lt allowed
• is
• Equal to
• Not equal to
• Really really equal to
• Identical to
• Identical the same in type and value

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Flow Control

• Supports
• if elseif else
• while
• do while
• switch
• for

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If

• if (expression) some statements
• if (expression) some statements
• else some more statements
• if (expression) some statements
• elseif (expression) some more statements
• else some more statements

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If

• if (var lt 0)
• echo(The variable has the negative value .
  var . ltpgt)
• elseif (var 0)
• echo(The variable has the value of zeroltpgt)
• else
• echo(The variable has the positive value .
  var . ltpgt)

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For loop

• for (expression1 expression2 expression3)
  statement
• Expression 1 is the start condition
• Expression 2 is the end condition
• Expression 3 is the increment operation
• for (c1 clt10 c)
• echo (c . ltbrgt)

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For loop

• for (c1 clt10 c)
• echo (c . ltbrgt)
• echo (c2 . ltbrgt)
• endfor
• Braces may also be used
• Use this in tutorial to create 12 times table
  page (with appropriate headers etc)

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While

• while (expression) some statements
• x1
• while (xlt10)
• echo(x . ltbrgt)
• x

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Do While

• do
• something
• while (expression)

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Switch

• switch (expression)
• case result1
• some statements
• break
• case result2
• some other statements
• break
• default
• something else

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Operators

• - / -- operators allowed
• ? ternary operator
• (expression) ? if_true if_false
• mood sad
• text ( moodhappy ) ? Hooray Leave me
  alone
• echo (ltbrgt . text)

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Summary

• PHP gives access to a lot of system information
• Operators in PHP are very similar to C
• - / -- ?
• comparison gt lt gt lt
• Flow Control in PHP is also very similar to C
• if, for, while, do while, switch