ITM 352 Data types, Variables

1. ITM 352Data types, Variables

2. Output in PHP • 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<br>line2';

3. $name $age What is a Variable? 'Dan' 30.3 • 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 $<identifier> • PHP Example: $name, $age • JS Example: var name, var age • Case sensitive!

4. 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 var count = 10;// initialize counter to ten var count = count - 1;// decrement counter • new value of count = 10 - 1 = 9

5. 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: • $test = 1.1 ; // declares and sets a real number • $test = true ; // declares and sets a boolean • $test = 'Zip Zap' ; // declares and sets a string • var a = 1.1 ; // declares and sets a real number • var a = true; // declares and sets a boolean • var a = 'Zip Zap' ; // declares and sets a string

6. 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) 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!

7. Variable Default Values • Variables have default values • $test = $test + 1; // $test=0 by default • $str = $str."Fred"; // default $str='' • var test = test + 1; // test=0 by default • var str = str + "Fred"; // default str="" • IMPORTANT: It is best to not assume the default value is what you want. Alwaysexplicitly set the initial value of a variable!!!! e.g. • $test = 0; $str = ""; $bool = false;

8. 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) Two Main Kinds of DataTypes 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

9. floating point real numbers, both positive and negative has a decimal point (fractional part) two formats number with decimal point, e.g. 514.061 e (or scientific, or floating-point) notation, e.g. 5.14061E2, which means 5.14061 x 102 In PHP these are referred to as double null The 'nothing' type (more on this later) 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

10. Which Ones to Know for Now – 2. • 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. JS not so much, but there are frameworks such as JQuery that do. • Manipulation, searching, comparing, translation, etc. • Check out php.net • Examples: “Mr. Smith”, ‘808-956-6948’, ‘21.7’, “1202 King St.”

11. 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; // $a is “unset”, also can use unset($a) • var a = null; // var a; would set a as “undefined” not null

12. 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: +, -, ., *, /, %

13. Simple Expressions With Variables • Variables can be operated on (e.g. arithmetic) // add 1 to value in $test and set in $add $add = $test + 1; // multiply $test by 2 and set in $mult $mult = $test * 2; // concatenate string in $str with 'Fred' and // set in $str $str = $str . " Fred";

14. Printf() • Use printf() for more complex formatted output printf('This prints 2 decimal places %.2f', 3.1415927); 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 %)