Slide môn học PHP session 4 functions in PHP

Functions in PHP Session 11 Review - I   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 statements are:  While Loop  Do-While Loop  For Loop PHP / Session 11 / Slide of 29 Review - II     While loop executes loop statements depending on the return result of the testing condition after testing it Testing condition in Do-While loop is placed after the loop ends For loop executes a set of codes repetitively for a specified amount of time Execution of the loops is controlled with the help of jump statements such as:  Break Statement  Continue Statement  Exit Statement PHP / Session 11 / Slide of 29 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 PHP / Session 11 / Slide of 29 Objectives  Use Functions  Use built in functions  Use user defined function  Pass arguments to function  Return values from functions  Use recursive functions PHP / Session 11 / Slide of 29 Functions     Function is block of code that has performs a specified job Function enables reusing the same piece of code in the program without typing it again 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 PHP / Session 11 / Slide of 29 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  Underscore A function name cannot contain the following:  Blank Spaces  Periods  Reserved words  Syntactical punctuation PHP / Session 11 / Slide of 29 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 PHP / Session 11 / Slide of 29 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 PHP / Session 11 / Slide of 29 Mathematical Functions - II Function General Form Description min(ar1, Returns the smallest value of the argument arg2, argn It also allows comparing multiple arrays ) For multiple arrays, main function compares form left to right sqrt sqrt(float arg) pow pow(number Returns the value of base raised to the base, power of exp number exp) Returns the square root of argument PHP / Session 11 / Slide 10 of 29 String Functions - IV Function ord General Form ord(string) Description Returns the ASCII value of the first character of the string The ord function is the complement of the chr function PHP / Session 11 / Slide 15 of 29 Date and Time Functions  The date and time functions enable us to obtain the date and time from the system Following table lists few of the date functions available: 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 PHP / Session 11 / Slide 16 of 29 Date and Time Functions - II Function time General Form time(void) strtotime Strtotime(string time [,int now]) Description Provides the current time measured in the number of seconds Accepts a string as the argument and formats it into a Unix timestamp relative to specified in the now argument PHP / Session 11 / Slide 17 of 29 Error Handling Functions- I   Error handling functions deal with errors They allow user to define the error handling rules Function debug_backtrace General Form Description debug_backtrace(vo Generates a PHP id) backtrace set_error_handler set_error_handler( callback error_handler [,int error_types] Sets a user function to handle errors in a script PHP / Session 11 / Slide 18 of 29 Error Handling Functions - II Function General Form error_reporting error_reporting( C onstant) trigger_error trigger_error(stri ng error_msg [,int error type] Description Sets which PHP errors are reported 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 PHP / Session 11 / Slide 19 of 29 Declaring a Function   A user can also define a function for performing a task To declare a function, the syntax is: function fun_name() { code } Where,  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 PHP / Session 11 / Slide 20 of 29 Passing arguments to function - I   A user may pass arguments to a function A user may pass values into three ways They are as follows:  Passing by value  Passing by reference  Setting default values PHP / Session 11 / Slide 21 of 29 Passing arguments to function - II  To define the function for passing parameters: function fun_name(arg1,arg2, ,argn) { code } Where,  fun_name - Specifies the name of the function  arg - Specifies the arguments that are passed to the function  code - Defines a valid PHP code PHP / Session 11 / Slide 22 of 29 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 PHP / Session 11 / Slide 23 of 29 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 PHP / Session 11 / Slide 24 of 29 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 PHP / Session 11 / Slide 25 of 29 Returning values from functions  A function can also return values  The return statement is used to return value from the function PHP / Session 11 / Slide 26 of 29 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 PHP / Session 11 / Slide 27 of 29 Recursion    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 PHP / Session 11 / Slide 28 of 29 Summary    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 Recursive functions calls it self Recursive functions are simpler to code PHP / Session 11 / Slide 29 of 29 [...]... using loops  Easy to understand at a later stage Disadvantage:  May require more time to execute as against the non recursive functions PHP / Session 11 / Slide 28 of 29 Summary    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. .. ASCII bin2hex bin2hex(strin g) Returns ASCII value This ASCII value is the hexadecimal representation of the string strtolo strtolower(st wer ring) Converts the string entered as the argument into lower case PHP / Session 11 / Slide 13 of 29 String Functions - III Function General Form Description strlen strlen(string) strcmp strcmp(string1,stri Returns zero if the string1 is ng2) equal to string2 It... 11 / Slide 16 of 29 Date and Time Functions - II Function time General Form time(void) strtotime Strtotime(string time [,int now]) Description Provides the current time measured in the number of seconds Accepts a string as the argument and formats it into a Unix timestamp relative to specified in the now argument PHP / Session 11 / Slide 17 of 29 Error Handling Functions- I   Error handling functions. .. specifies to PHP that the code following it is function  fun_name - Specifies the name of the function  code - Defines the valid PHP code PHP / Session 11 / Slide 20 of 29 Passing arguments to function - I   A user may pass arguments to a function A user may pass values into three ways They are as follows:  Passing by value  Passing by reference  Setting default values PHP / Session 11 / Slide 21... string1 is less than the string2 Otherwise, it returns greater than zero Returns the length of the string specified as argument PHP / Session 11 / Slide 14 of 29 String Functions - IV Function ord General Form ord(string) Description Returns the ASCII value of the first character of the string The ord function is the complement of the chr function PHP / Session 11 / Slide 15 of 29 Date and Time Functions. .. 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 the argument into lower case PHP / Session 11 / Slide 12 of 29 String Functions - II Function chr General Form chr(int ascii) Description... 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 PHP / Session 11 / Slide 11 of 29 String Functions - I   String functions operate on character type of data Following table lists few of the string functions available in PHP. .. reference PHP / Session 11 / Slide 24 of 29 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 PHP / Session 11 / Slide 25 of 29 Returning values from functions  A function can also return values  The return statement is used to return value from the function PHP / Session 11 / Slide. .. 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 PHP / Session 11 / Slide 27 of 29 Recursion    When a function calls itself, it is termed as recursion Advantage:  Simpler to code compared to non recursive functions, ... allow user to define the error handling rules Function debug_backtrace General Form Description debug_backtrace(vo Generates a PHP id) backtrace set_error_handler set_error_handler( callback error_handler [,int error_types] Sets a user function to handle errors in a script PHP / Session 11 / Slide 18 of 29 Error Handling Functions - II Function General Form error_reporting error_reporting( C onstant)