ITM 352 Data Types and Variables

Transcript

1. ITM 352 - © Port, Kazman Variables - 1 ITM 352 Data types, Variables
2. ITM 352 - © Port, Kazman Variables - 2 Announcements ❒ Apache and NetBeans must be installed and working on your own machine ❒ Start NetBeans now! ❒ Do lab exercises (on class website) when indicated ❍ Submit answers to Laulima
3. ITM 352 - © Port, Kazman Variables - 3 Agenda ❒ Lecture: ❍ Data types ❍ Variables ❍ Outputting to the console and screen
4. ITM 352 - © Port, Kazman Variables - 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 $<identifier> ❍  PHP Example: $name, $age ❍  JS Example: var name, var age ❍  Case sensitive! $name var age 'Dan' 30.3
5. ITM 352 - © Port, Kazman Variables - 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 var count = 10;// initialize counter to ten var count = count - 1; // decrement counter ❍  new value of count = 10 - 1 = 9
6. ITM 352 - © Port, Kazman Variables - 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 ❍  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
7. ITM 352 - © Port, Kazman Variables - 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)
8. ITM 352 - © Port, Kazman Variables - 8 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;
9. ITM 352 - © Port, Kazman Variables - 9 Echo/Print (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';
10. ITM 352 - © Port, Kazman Variables - 10 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)
11. ITM 352 - © Port, Kazman Variables - 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. 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)
12. ITM 352 - © Port, Kazman Variables - 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”, ‘808-956-6948’, ‘21.7’, “1202 King St.” Which Ones to Know for Now – 2.
13. ITM 352 - © Port, Kazman Variables - 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
14. ITM 352 - © Port, Kazman Variables - 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: +, -, ., *, /, %
15. ITM 352 - © Port, Kazman Variables - 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";
16. ITM 352 - © Port, Kazman Variables - 16 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 %) Do Exercise #2,#3 (and bonus if you wish) in lab