CSCI 116 Week 3 Functions

1
CSCI 116 Week 3 Functions Control Structures
2
Topics

• Using functions
• Variable scope and autoglobals
• Decision logic
• if statements
• if...else statements
• switch statements
• Loops
• while statements
• do...while statements
• for and foreach statements

3
Defining Functions

• Functions
• Groups of statements that you can execute as a
  single unit
• Defining a function
• lt?php
• function name_of_function(parameters)
• statements
• ?gt

4
Function Parameters

• A parameter is an input to the function
• Parameters are placed within the parentheses that
  follow the function name
• Not all functions accept parameters

function average(num1, num2)
2 parameters
function printHello()
0 parameters
function calcTax(price)
1 parameter
5
Function Example

• function printPhrase(phrase)
• echo phraselt/ brgt
• printPhrase(Silly goose!)

6
Returning Values

• A return statement returns a value to the
  statement that called the function
• A function does not have to return a value
• function averageNumbers(a, b, c)
• sumOfNumbers a b c
• average sumOfNumbers / 3
• return average

7
Function Practice

1. Write a function that takes a name and prints
   Hello, name!
2. Write a function that returns the maximum of two
   values.
3. Write a function that converts celsius to
   fahrenheit (FC1.832).
4. Write a function that takes a radius and returns
   the circumference of a circle (CPIDiameter).

8
Understanding Variable Scope

• Variable scope
• Where in your program a declared variable can be
  used
• Can be either global or local
• Global variable
• Declared outside a function and available to all
  parts of your program
• Local variable
• Declared inside a function and only available
  within that function

9
Variable Scope

• lt?php
• globalVar "Global"
• function scopeExample()
• echo "ltbgtInside function ltbr /gtlt/bgt"
• localVar "Local"
• echo "localVarltbr /gt"
• global globalVar
• echo "globalVarltbr /gtltbr /gt"
• scopeExample()
• echo "ltbgtOutside function ltbr /gtlt/bgt"
• echo "localVarltbr /gt"
• echo "globalVarltbr /gt"
• ?gt

global keyword used inside function to
reference global variable
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Autoglobals

• PHP includes predefined global arrays, called
  autoglobals or superglobals
• Autoglobals contain client, server, and
  environment information
• Autoglobals are associative arrays
• Elements are referred to with an alphanumeric key
  instead of an index number
• Example _SERVERPHP_SELF

11
PHP Autoglobals
See http//us.php.net/reserved.variables for more
information.
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Using GLOBALS
lt?php globalVar "Global" function
scopeExample() echo "ltbgtInside functionltbr
/gtlt/bgt" localVar "Local" echo
"localVarltbr /gt" echo GLOBALS"globalVar" ,
"ltbr /gtltbr /gt" scopeExample() echo
"ltbgtOutside functionltbr /gtlt/bgt" echo
"localVarltbr /gt" echo "globalVarltbr /gt" ?gt
13
Using _SERVER

• lt?php
• echo "The name of the current script is ",
  _SERVER"PHP_SELF", "ltbr /gt"
• echo "The absolute path of the current script
  is ", _SERVER"SCRIPT_FILENAME", "ltbr /gt"
• echo "The name of the server on which this
  script is executing is ", _SERVER"SERVER_NAME"
  , "ltbr /gt"
• echo "This script was executed with the
  following server software ", _SERVER"SERVER_SOF
  TWARE", "ltbr /gt"
• echo "This script was executed with the
  following server protocol ", _SERVER"SERVER_PRO
  TOCOL"
• ?gt

14
Using _GET and _POST

• _GET and _POST allow you to access the values
  of forms that are submitted to a PHP script
• _GET appends form data as one long string to the
  URL
• _POST sends form data as a transmission separate
  from the URL

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_GET Example
ltform method"get" action"processForm.php"gt N
amenbspltinput type"text" name"name" size"20"
/gtltbr /gt Hometownnbspltinput type"text"
name"town" size"20" /gtltbr /gt ltinput
type"submit" value"Submit"gt lt/formgt
lt?php echo "Hello, ", _GET"name", " from ",
_GET"town", "!" ?gt
Note the values in the URL
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_POST Example
ltform methodpost" action"processForm.php"gt
Namenbspltinput type"text" name"name"
size"20" /gtltbr /gt Hometownnbspltinput
type"text" name"town" size"20" /gtltbr
/gt ltinput type"submit" value"Submit"gt lt/formgt

lt?php echo "Hello, ", _POST"name", " from ",
_POST"town", "!" ?gt
No values in the URL
17
if Statements

• Used to execute specific programming code if a
  condition returns true
• Syntax
• if (conditional expression)
• statement
• Example
• num 5
• if (num 5) // CONDITION IS TRUE
• echo The condition evaluates to true.lt/ brgt
• echo 'num is equal to ', num.lt/ brgt
• echo This statement always executes.lt/ brgt

18
if...else Statements

• An else clause executes when the condition in an
  if...else statement evaluates to false
• Syntax
• if (conditional expression)
• statement
• else
• statement
• Example
• Today Tuesday
• if (Today Monday)
• echo Today is Mondaylt/ brgt
• else
• echo Today is not Mondaylt/ brgt

Curly braces are not required when there is only
one statement after the if or else.
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Nested if Statements

• One decision-making statement may be contained
  within another
• if (_GETSalesTotal gt 50)
• if (_GETSalesTotal lt 100)
• echo Sales total is between 50 and 100.lt/
  brgt

20
switch Statements

• Controls program flow by executing a specific set
  of statements depending on the value of an
  expression
• Compares the value of an expression to a value in
  a case label
• case label can be followed by one or more
  statements
• Each set of statements is usually followed by the
  keyword break
• The default label contains statements that
  execute when the value of the expression does not
  match any other case label

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switch Statements

• Syntax
• Switch (expression)
• case label statement(s)
• break
• case label
• statement(s)
• break
• ...
• default
• statement(s)

• Example
• Switch (day)
• case 1
• print partridge
• break
• case 2
• print turtle doves
• break
• ...
• default
• print Invalid

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Decision Practice

• Write a statement that prints even if a
  variable num is even.
• Write a statement that prints even if a
  variable num is even, and odd otherwise.
• Write a statement that prints A for a grade of
  90-100, B for 80-89, C for 70-79, D for
  60-69 and F otherwise.
• Write a switch statement that takes a number and
  prints the corresponding month, e.g. January
  for 1.

23
Repeating Code

• A loop statement is a control structure that
  repeatedly executes a statement or a series of
  statements
• Each repetition of a loop is called an iteration
• Loop may execute while a condition is true or
  until a condition becomes true
• Four types of loops
• while statements
• do...while statements
• for statements
• foreach statements

24
while Statements

• Repeats one or more statements while a
  conditional expression evaluates to true
• Syntax
• while (conditional expression)
• statement(s)

25
while Statement Example

• Count 1
• while (Count lt 5)
• echo Countltbr /gt
• Count
• echo You have printed 5 numbers.lt/ brgt

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while Statement Example

• Count 10
• while (Count gt 0)
• echo Countltbr /gt
• --Count
• echo We have liftoff.lt/ brgt

27
while Statements Example

• Count 1
• while (Count lt 100)
• echo Countltbr /gt
• Count 2

28
Infinite Loops

• In an infinite loop, a loop statement never ends
  because its conditional expression is never false
• Count 1
• while (Count lt 10)
• echo The number is Count

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do...while Statements

• Executes a statement or statements at least once
• Repeats execution as long as conditional
  expression is true
• Syntax
• do
• statement(s)
• while (conditional expression)

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do...while Example

• Count 2
• do
• echo The count is equal
• to Countlt/ brgt
• Count
• while (Count lt 2)

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do...while Example

• DaysOfWeek array(Monday, Tuesday,
  Wednesday, Thursday, Friday, Saturday,
  Sunday)
• Count 0
• do
• echo DaysOfWeekCount, ltbr /gt
• Count
• while (Count lt 7)

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for Statements

• Used to repeat one or more statements as long as
  a given condition is true
• Includes code that initializes a counter and
  changes its value with each iteration
• Syntax
• for (counter declaration and initialization
  condition update statement)
• statement(s)

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for Statements Example

• FastFoods array(pizza, burgers, french
  fries, tacos, fried chicken)
• for (Count 0 Count lt 5 Count)
• echo FastFoodsCount, ltbr /gt

34
foreach Statements

• Used to iterate or loop through the elements in
  an array
• Does not require a counter
• Specify an array expression within a set of
  parentheses following foreach
• Syntax
• foreach (array_name as variable_name)
• statements

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foreach Example

• animals array(lion, tiger, monkey)
• foreach (animals as animal)
• echo animalltbr /gt

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Loop Practice

• Using a do loop, dowhile loop, and for loop,
  perform each of the following tasks
• Print the numbers from 10 to 1 and then
  Blastoff!
• Add up the numbers from 1 to 10 and then display
  the result.

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Summary

• Functions are groups of statements that you can
  execute as a single unit
• Autoglobals contain client, server, and
  environment information
• Flow control determines the order in which
  program statements execute
• Decision logic includes if, ifelse, and switch
• Loops include while, dowhile, for, and foreach