Slide môn học PHP session 4 functions in PHP

Following table lists few of the built in mathematical functions available: Function General Form Description abs absarg Returns the absolute value of the argument max maxarg1,arg2,… arg

Functions in PHP

Session 11

 Loop is executed depending on the return value of the

testing conditions by testing it

 Different types of looping statements hold the

iterations of the loops The different types of looping

 Execution of the loops is controlled with the help of jump

statements such as:

 Break Statement

 Continue Statement

 Exit Statement

Review - III

 Break statement stops the iteration of the loop from

the current loop execution

 Continue statement is used for breaking the iteration

of the loop from the current loop execution

 Exit statement is used to break the loop while the loop

is in the execution process

 Use Functions

 Use built in functions

 Use user defined function

 Pass arguments to function

 Return values from functions

 Use recursive functions

 Function helps us in making a program organized

 Functions enhance the logical flow in a program by dividing up complicated code sequences into smaller modules

Naming Conventions for

Functions

 A valid function name may contain:

 Characters from A-Z

 Numbers form 0-9 A function name cannot start with a number.

Built - in Functions

 PHP has built in functions within it

 Built in functions can work with databases, numbers, strings, arrays, dates and time, and email

 Whenever the function is been called they are

compiled directly in PHP

Mathematical Functions - I

 Mathematical functions operate on numerical data Following table lists few of the built in mathematical functions available:

Function General Form Description

abs abs(arg) Returns the absolute value of the argument

max max(arg1,arg2,…

argn) max(array[])

Returns the largest value of the specified arguments It also allows comparing multiple arrays For multiple arrays, max function compares from left to right

Mathematical Functions - II

Function General Form Description

min min(ar1,

arg2, argn)

Returns the smallest value of the argument

It also allows comparing multiple arrays For multiple arrays, main function compares form left to right

Returns the value of base raised to the power of exp

Mathematical Functions - III

Function General Form Description

pow pow(number

base, number exp)

Returns the value of base raised to the power of exp

round round(float

val [,int precision)

Returns the rounded value of the argument specified

String Functions - I

 String functions operate on character type of data

 Following table lists few of the string functions available in PHP:

Function General Form Description

chr chr(int ascii) Returns the character

equivalent to the specified as the ASCII

bin2hex bin2hex(string) Returns ASCII value This

ASCII value is the hexadecimal representation of the string

strtolower strtolower(string) Converts the string entered as

Returns ASCII value This ASCII value

is the hexadecimal representation of the string

strtolo strtolower(st Converts the string entered as the

String Functions - III

Function General Form Description

strlen strlen(string) Returns the length of the string

specified as argumentstrcmp strcmp(string1,stri

ng2)

Returns zero if the string1 is equal to string2 It returns less than zero, if the string1 is less than the string2 Otherwise, it returns greater than zero

String Functions - IV

Function General Form Description

ord ord(string) Returns the ASCII value of

the first character of the string The ord function is the complement of the chr function

Date and Time Functions

Function General Form Description

checkdate checkdate(month,da

y,year)

Returns the value as TRUE, only if the given value is valid It will return a FALSE value, if the date is invalid

getdate getdate(timestamp) Parses an English datetime

format into a UNIX timestamp

Date and Time Functions - II

Function General Form Description

time time(void) Provides the current time

measured in the number of seconds

strtotime Strtotime(string

time [,int now])

Accepts a string as the argument and formats it into

a Unix timestamp relative to specified in the now

argument

Error Handling Functions- I

 Error handling functions deal with errors

 They allow user to define the error handling rules

Function General Form Description

debug_backtrace debug_backtrace(vo

id)

Generates a PHP backtrace

set_error_handler set_error_handler(

callback error_handler [,int error_types]

Sets a user function to handle errors in a script

Error Handling Functions - II

Function General Form Description

Used to activate a user error condition This function is useful when we want to generate a particular response to some error

at run time

Declaring a Function

 A user can also define a function for performing a task

 To declare a function, the syntax is:

 function - is a keyword that specifies to PHP that the

code following it is function

 fun_name - Specifies the name of the function

 code - Defines the valid PHP code

Passing arguments to function - I

 A user may pass arguments to a function

 A user may pass values into three ways They are as

Passing arguments to function - II

 To define the function for passing parameters:

 fun_name - Specifies the name of the function

 arg - Specifies the arguments that are passed to the

function

 code - Defines a valid PHP code

Passing Argument by value

 Value of the argument remains unchanged outside

the function if we pass the arguments by value

 If we wish to allow a function to modify its

arguments, we must pass them by reference

 When a function is defined, the $ sign is used with

the arguments to indicate that the argument is

passed by value

Passing Value by reference

 We can also pass the value by reference

 If the value is passed by reference then the value is

modified even outside the function

 When the function is defined, the ‘&’ sign is used

along with the parameters to indicate that the value is

passed by reference

Setting default parameters

 We can also assign default values to the parameters

 We assign a default value to the argument at the place

where the function is declared

Returning values from functions

 A function can also return values

 The return statement is used to return value from

the function

Nesting of Functions

 A function enables to divide a program into modules

 These modules may be interdependent and may

require interaction between them

 When one function calls several other functions, it is

termed nesting of functions

 When a function calls itself, it is termed as recursion

 Advantage:

 Simpler to code compared to non recursive functions,

which are implemented using loops

 Easy to understand at a later stage

 Disadvantage:

 May require more time to execute as against the non

recursive functions

 Functions are used to avoid rewriting the codes again and again

 We have built-in functions in PHP

 The built-in functions can be categorized as:

 Mathematical Functions

 String Functions

 Date and Time Functions

 Error Handling Functions

 A user can also define a function

 We can pass arguments to a function

 We can pass arguments to a function by value, reference, or even pass default values to a function