ITM © Port, KazmanVariables - 1 ITM 352 Data types, Variables Class #4

ITM © Port, KazmanVariables - 2 Announcements  Apache and NetBeans must be installed and working on your own machine  Start NetBeans and download Lab 4 from the class server now!

ITM © Port, KazmanVariables - 3 Agenda  Lecture:  Outputting to the screen  Data types  Variables

ITM © Port, KazmanVariables - 4 What is a Variable?  A named location to store data  a container for data (like a box or bucket)  It can hold only one type of data at a time  for example only integers, only floating point (real) numbers, or only characters  A variable with a scalar type holds one scalar value  A variable with a compound type holds multiple scalar values, BUT the variable still holds only a single (the compound type itself) value  Syntax for a variable is $  Example: $name, $age  Case sensitive! $name $age 'Dan'30.3

ITM © Port, KazmanVariables - 5 Assigning Values to Variables  The assignment operator: "="  "sets" a value for a variable  not the "is equal to" sign; not the same as in algebra  It means - "Assign the value of the expression on the right side to the variable on the left side."  Can have the variable on both sides of the equals sign: $count = 10;// initialize counter to ten $count = $count - 1;// decrement counter  new value of count = = 9

ITM © Port, KazmanVariables - 6 Creating Variables  A variable is declared the first time a value is set for it  A variable declaration associates a name with a storage location in memory and specifies the type of data it will store:  $a = 1.1 ;// declares and sets a real number  $a = true ;// declares and sets a boolean  $a = 'Zip Zap' ; // declares and sets a string

ITM © Port, KazmanVariables - 7 Variable Names: Identifiers Rules (these must be obeyed)  all identifiers must follow the same rules  must not start with a digit  must contain only numbers, letters, underscore (_) and some other special characters  names are case-sensitive (ThisName and thisName are two different variable names)  No spaces! Good Programming Practice (these should be obeyed)  always use meaningful names from the problem domain (for example, eggsPerBasket instead of n, which is meaningless, or count, which is not meaningful enough)  start variable names with lower case  capitalize interior words (use eggsPerBasket instead of eggsperbasket )  use underscore (_) for spaces  CAPITALIZE constants (i.e. variables that do not change values)

ITM © Port, KazmanVariables - 8 Variable Default Values  Variables have default values  $a = $a + 1; // $a=0 by default  $s = $s."Fred"; // default $s=""  IMPORTANT: It is best to not assume the default value is what you want. Always explicitly set the initial value of a variable!!!! e.g.  $a = 0; $s = ""; $b = false;

ITM © Port, KazmanVariables - 9 Echo/Print  Use echo for simple output  echo 'hello';  echo 'hello', ' goodbye';  echo ('hello');  print is virtually the same syntax  print 'hello';  You can use () if you like  echo('hello');  print('hello');  New line for console output (we don’t do much of this)  echo " line1\nline2 " ;  New line for HTML output  echo 'line1 line2';

ITM © Port, KazmanVariables - 10 Two Main Kinds of Data Types in PHP Scalar  the simplest types  also called "primitive" or "basic" types  cannot decompose into other types  contain single values only  Examples:  Integer  Floating point (real)  String  Boolean Compound also call class types  more complex  composed of other types (primitive or class types)  can contain multiple values  Examples:  Arrays  Objects (more about these in ITM353)

ITM © Port, KazmanVariables - 11 Which Ones to Know for Now - 1  integer  just whole numbers  may be positive or negative  no decimal point  may use  Octal: 0755 // starts '0'  Hex: 0xFF // starts '0x'  In PHP these are referred to as int  boolean  only two values – true or false  used for 'conditional' tests (e.g. if, when )  In PHP these are referred to as bool  floating point  real numbers, both positive and negative  has a decimal point (fractional part)  two formats  number with decimal point, e.g  e (or scientific, or floating-point) notation, e.g E2, which means x 10 2  In PHP these are referred to as double  null  The 'nothing' type (more on this later)

ITM © Port, KazmanVariables - 12  A string is a sequence of characters  A very common data type  Names, passwords, addresses, histories, etc.  Often used to represent complex data  Dates, phone numbers, SS numbers, formatted output  A common data-interchange or data-sharing type  key-value pairs, XML, comma delimited data, logs  PHP has a vast and powerful set of functions for working with strings  Manipulation, searching, comparing, translation, etc.  Check out php.net  Examples: “Mr. Smith”, ‘ ’, ‘21.7’, “1202 King St.” Which Ones to Know for Now – 2.

ITM © Port, KazmanVariables - 13 NULL  Null is a special type that means "no value"  It can be used to unset a variable  It is used as a place holder within compound types (more on this later…)  $a = NULL; // $a is unset Do Exercise #1 in lab

ITM © Port, KazmanVariables - 14 Simple Expressions  Data types can be operated on (e.g. arithmetic, string operations) echo 1+2; echo 3*2; echo "Big". " ". "Dude"; printf("5/3 is about %3d", 5/3); Operators: +, -,., *, /, %

ITM © Port, KazmanVariables - 15 Simple Expressions With Variables  Variables can be operated on (e.g. arithmetic) // add 1 to value in $a and set in $add $add = $a + 1; // multiply value in $a by 2 and set in $mult $mult = $a * 2; // concatenate string in $s with 'Fred' and // set in $str $str = $s. " Fred";

ITM © Port, KazmanVariables - 16 Printf()  Use printf() for more complex formatted output printf('This prints 2 decimal places %.2f', ); This prints 2 decimal places 3.14  Printf() is a function whose first argument is a string that describes the desired format and the remaining arguments are the values to substitute into the type specifications (anything that starts with %) Do Exercise #2,#3 (and bonus if you wish) in lab