1. ITM 352 Data 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. 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 $<identifier>
PHP Example: $name, $age
JS Example: var name, var age
Case sensitive!
$name
'Dan'
$age
30.3

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 = = 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:
$a = 1.1 ; // declares and sets a real number
$a = true ; // declares and sets a boolean
$a = '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. 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)

7. Variable Default Values
Variables have default values
$a = $a + 1; // $a=0 by default
$s = $s."Fred"; // default $s=''
var a = a + 1; // a=0 by default
var 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;

8. Two Main Kinds of Data Types
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)

9. 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 102
In PHP these are referred to as double
null
The 'nothing' type (more on this later)

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”, ‘ ’, ‘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
Do Exercise #1 in lab

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 $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";

14. Do Exercise #2,#3 (and bonus if you wish) in lab
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