1 Session 3: Flow Control & Functions iNET Academy Open Source Web Programming

2 Objectives Discuss about expressions & operators Discuss about conditional statements Discuss about loop statements Discuss about calling & defining functions

3 Expressions A statement is code that performs a task Statements are made up of epressions and operators An expression is a piece of code that evaluates to a value An operator is a code element that acts on an expression in some way

4 Operators PHP has many types of operators, including Arithmetic operators Array operators Assignment operators Bitwise operators Comparison operators Execution operators Increment/decrement operators Logical operators String operators An operator has four properties Number of operands Type of operands Order of precedent Operator associativity

5 Operators (cont.) Number of Operands Binary operators: combine two expressions into a single expression Unary operators: take only one operand Negation operator (-) Preincrement and predecrement Ternary operator: takes three operator

6 Operators (cont.) Types of Operands Certain operators expect their operands to be of particular data types PHP automatically convert operands to the expected data types. But there are times, conversions are impossible. Eg: “Becker”*”Furniture” ; “80” * “70” To set or convert a variable’s type using settype to change the data type actually casting temporarily converts the value

7 Operators (cont.) Order of Precedence Determines which operator processes first in an expression Eg: * and / before + and – If operators have the same precedence, they are processed in the order they appear in the expression Use ( and ) to change the precendence

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9 Operators (cont.) Relational operators: used to compare two operands and return either TRUE or FALSE value. Equality operator (==) only checks whether the values are the same. Data type conversion may be required Eg: “1” == 1 return TRUE (===) checks whether the values and types are the same. Eg: ‘1’ === 1 returns FALSE Inequality operator != checks for the opposite of equality Comparison operators:, >= Logical operators

10 Conditionals There are three conditionals in PHP If ? : : (shorthand for an if statement) switch

11 The if statement Common true conditions $var, if $var is not an empty set (0), an empty string, or NULL Isset($var) if $var is not NULL, an empty string or an empty set An expression return TRUE

12 The elseif statement

13 The ? operator

14 The switch statement Compares an expression to numerous values

15 The switch statement (cont.) Breaking out: using break keyword

16 The switch statement (cont.) Defaulting

17 Looping While For Do … while

18 While loops

19 Do.. While loops

20 For loops

21 Breaking Out of a Loop Use break statement

22 Continue Statement Stop processing the current block of code and jump to the next iteration of the loop

23 Functions Create & execute a function Send values to a function Return values from a function Verify if a function exists

24 Calling Functions To call a function Write the name of the function An opening parenthesis ( The parameters A closing parenthesis Function’s name are not case-sensitive Most functions have return values

25 Defining Functions Four elements of a function’s definition 1 – the function keyword 2 – the function’s name 3 – the arguments are optional 4 – the code of the function Function can be defined and called anywhere

26 Parameters Information pass to a function Parameter’s definition Type of data: don’t have to define Parameter’s names must be specified

27 Parameters (cont.) Parameters can have default values

28 Parameters (cont.) Parameter Reference: pass the reference to value, not pass the value

29 Including and Requiring PHP files Place functions in a separate file to make code more readable PHP provides four functions include require include_once require_once The include statement: include and attach other PHP scripts to your scripts Include files should use.php extension instead of other extensions like.inc because of security reason

30 Including and Requiring PHP files (cont.) The include_once statement: prevent inlcuding many nested PHP scripts

31 Including and Requiring PHP files (cont.) require and require_once functions When using include and include_once, if the including PHP files is not exist, PHP post a warning and try to execute the program Require and require_once is used to make sure that a file is included and to stop the program if it isn’t

32 Testing a function To check for the existence of functions, use the function function_exist() It takes a parameter as the function’s name Return TRUE or FALSE depending on whether the function has been defined

33 Practice In this practice, you will: Ex1: Write a loop using the “for” loop to print all even numbers which are less than 50 Ex2: Same task as Ex1, but using the “while” loop Ex3: Write a program to find prime numbers which are less than 100. Display them in each rows. Ex4: Print the prime numbers from Ex3 in a table, each rows has 10 numbers. Ex5: Write a program that includes previous exercises. Use a variable name $flag. If $flag==1 then include Ex1 If $flag==2 then include Ex2 If $flag==3 then include Ex3 If $flag==4 then include Ex4 Ex6: Pack Ex1-Ex4 into four functions. Use the same routine as Ex5.