8/28/12 Chapter 1 – PHP Crash Course Metropolitan State University ICS 325 Internet Application Development
Class Notes – Chapter 1 – PHP Crash Course
What is PHP? PHP is a server side scripting language, written specifically for the Web PHP was developed in 1994 by Rasmus Lerdorf PHP originally stood for Personal Home Page PHP currently stands for PHP Hypertext Preprocessor Current version of PHP is 4.3.6 Version 5 is available for early adopters Home page = http://www.php.net PHP strengths include: High performance, Interfacing with Different DBMS (uses ODBC), Libraries, Low Cost, Portability, open source, and thousands of functions. Web server must have PHP installed. PHP scripts are interpreted and executed on the server. Output from a PHP script looks like plain old HTML. The client cannot see your PHP code, only its output.
PHP Tags – Short Style Short Style
”; ?> XML Style XML Style”); ?> Script Style ASP Style <% echo “ASP Style
”; %>PHP Comments – C Style /* this is a multi line comment */ C++ Style // this is a single line comment PERL Style # this is a single line comment
Most PHP code statements must end with a ; (semi-colon) Conditionals and loops are an exception to the rule Variables: All variables in PHP begin with $ (dollar sign) All variables are created the first time they are assigned a value. PHP does not require you to declare variables before using them. PHP variables are multi-type (may contain different data types at different times) cs.metrostate.edu/~f itzgesu/courses/ics325/f all04/Ch01Notes.htm 1/9 8/28/12 Chapter 1 – PHP Crash Course Variables from a form are the name of the attribute from the submitting form. Can have any length, may consist of letters, numbers, underscores, and $ Cannot start with a digit Are case sensitive Can have the same name as built-in functions, but avoid doing so.
PHP’s data types: Integer (whole numbers) Float (real numbers) String (text enclosed in single or double quotes) Boolean (true or false) Object (instance of a class) Array (group of values, usually of the same type) Resource (external data source i.e. database record) Null (null – for undeclared, uninitialized variables or those set to NULL) Integers: Integers can be specified in decimal notation, optionally preceded by a sign (- or +). octal (8-based) notation is preceded with a 0, optionally preceded by a sign (- or +). hexadecimal notation precedes the number with 0x. $a = 1234; # decimal number $a = -123; # a negative number $a = 0123; # octal number (equivalent to 83 decimal) $a = 0x1A; # hexadecimal number (equivalent to 26 decimal)
Floats: (a.k.a. doubles, real numbers): Floating point numbers can be specified using any of the following syntaxes: $a = 1.234; $a = 1.2e3; $a = 7E-10; The size of a float is platform-dependent, although a maximum of ~1.8e308 with a precision of roughly 14 decimal digits is a common value (that's 64 bit IEEE format).
Strings: Strings are placed between quotes ( ‘ ) or double quotes ( “ ). The string concatenation operator is a dot (.) The escape character is a back slash(\) A string can be specified in three different ways:
1. Single quotes
cs.metrostate.edu/~f itzgesu/courses/ics325/f all04/Ch01Notes.htm 2/9 8/28/12 Chapter 1 – PHP Crash Course echo 'this is a simple string
'; // this is a simple string echo 'I\'ll be back
'; // output: ... I'll be back echo ‘delete C:\\*.*?
'; // output: ... delete C:\*.*? echo ‘You entered $value’; // You entered $value ?> Note: Variables will not be evaluated when they occur in single quoted strings.
2. Double quotes: If the string is enclosed in double-quotes ("), PHP understands more escape sequences for special characters: \n new line \r carriage return \t horizontal tab \\ backslash \$ dollar sign \” double quote
3. Heredoc syntax: Heredoc text behaves just like a double-quoted string except the string can span across multiple consecutive lines, without the double-quotes.
Note: No comments can go within the heredoc statement or they become part of it
Boolean: To specify a Boolean you can use the keywords true or false: $formOK = true; Other PHP variables will return Boolean values: The integer 0, the float 0.0, the string “0”, the empty string, an array w/zero elements, an object w/zero elements, and NULL, all evaluate to FALSE.
Every other value is considered TRUE. $x = -1; if($x) //evaluates to true.
cs.metrostate.edu/~f itzgesu/courses/ics325/f all04/Ch01Notes.htm 3/9 8/28/12 Chapter 1 – PHP Crash Course
Object: An instance of a class, use the new keyword to instantiate a class object. class Test { function doTest( ) { print (“doing the test”); } } $myTest = new Test( ); $myTest->doTest( ); //the object->method syntax
Arrays: an ordered map. You can map values using key, value pairs or numbered indices. Arrays in PHP can be used as hashes, vectors, stacks, queues, etc. $arr = array(“fruit”=>”apple”, “vegetable”=>”potato”); //key-value indices $arr = array(“apples”, “oranges”, “bananas”); //number indices
Null: Any variable that has no value or has been assigned the constant NULL: $x ; print ("x is ".getType($x)); //outputs: x is NULL
Embedding PHP in HTML: PHP may be embedded directly into HTML and is inserted between scripting delimiters: PHP tags allow the programmer to “escape” from HTML. PHP tags allow the programmer to insert PHP values into html With PHP, all statements end with a semicolon (;) PHP code is never visible to the client; instead, the PHP interpreter outputs the scripts statements. (print, echo)
…. ….
or
”; …
cs.metrostate.edu/~f itzgesu/courses/ics325/f all04/Ch01Notes.htm 4/9 8/28/12 Chapter 1 – PHP Crash Course $name = “Bob”; echo “
PHP’s Predefined Variables: $PHP_SELF the filename of the current script.
To access the text field use $Name = $myText Note: If globals were off, the way to access these variables would be: $Name = $HTTP_POST_VARS[“myText”]; // or $_POST[“myText”]
Note: Currently PHP does not recognize html attribute “id”, so will result in variable firstName not being submitted.
cs.metrostate.edu/~f itzgesu/courses/ics325/f all04/Ch01Notes.htm 5/9 8/28/12 Chapter 1 – PHP Crash Course Type Casting Because PHP is a weakly typed language we can use type casting to ensure correct data in a variable. Type casting sets the data type for a variable PHP automatically assumes the correct data type $money = 0; $correctMoney = (double)$money;
Constants Constants are variables that can also store any value, but cannot be reset. Once a constant is set in a script it cannot be modified. define(“SCHOOL”, “Metropolitan State University”); Do NOT use the $ (dollar sign) while referring to a constant. echo SCHOOL;
Variable Scope: Global: declared inside the script, visible throughout the script but not inside functions. Local: variables declared or used within functions.
Operators: Mathematic Operators +, -, *, /, and % (See Table 1.1 for other examples) $value1 = 10; $value2 = 8; $remainder = $value1 % $value2;
echo $remainder // value of 2 is display on screen If you apply arithmetic operators to strings, PHP will look for and convert any digits at the start of the string. If there are no digits, PHP will use 0. String Operators The only string operator in PHP is the concatenation operator The concatenation operator is denoted by a . (dot). $value1 = “This class is located at: “; $value2 = “St. Paul Campus”; $stringValue = $value1 . $value2;
echo $stringValue // This class is located at: St. Paul Campus - is display on screen
Assignment Operators PHP has a few different assignment operators cs.metrostate.edu/~f itzgesu/courses/ics325/f all04/Ch01Notes.htm 6/9 Chapter 1 – PHP Crash Course The standard assignment operator = Combination assignment operators +=, -=, *=, /=, %=, and .= (See Table1.2 for other examples) The Pre and Post Increment and Decrement operators -- ++
The combination assignment operators are shorthand notation for performing an operation and assigning the value to the current variable. $value *= 2; this statement is equivalent to the following $value1 = $value1 * 2;
The Pre and Post Increment and Decrement operators increment or decrement the current value by one. The value is changed before an operation happens with the Pre Increment and Decrement operators The value is changed after an operation happens with the Post Increment and Decrement operators $value = 5; echo ++$value; // Pre Increment – output would be 6 – current value = 6 echo $value--; // Post Increment – output would be 6 – current value = 5 Comparison Operators ==, ===, !=, <>, <, >, <=, and >= See Table 1.3 for other examples Remember Comparison == Assignment = if ($value1 == $value2){…
Logical Operators !, &&, ||, and, and or See table 1.4 for other examples if ($value1 == $value2) || ($value1 == $value3){… && and (and) provide the same service, except (and) has a lower order of precedence || and (or) provide the same service, except (or) has a lower order of precedence
See Table 1.6 for order of precedence Values are passed by copy in PHP. Use the reference operator ( & ) to pass values by reference:
cs.metrostate.edu/~f itzgesu/courses/ics325/f all04/Ch01Notes.htm 7/9 8/28/12 Chapter 1 – PHP Crash Course Ternary operator: condition? value if true: value if false; $c= ($a==5? true: false); //this operator does not nest as in Java
Error Suppressor Operator @ The error suppressor operator can be used in front of any expression that could potentially contain an error. The Error Suppressor suppresses errors. $value = @(21/0); NOTE: If you suppress your errors, you should write other code to handle the errors.
Variable Status Checking PHP has built in functions for checking the status of variables isset returns true if the variable has been created, false otherwise unset deletes the variable empty checks to see if the variable is empty if so returns true Conditional Statements PHP supports all control structures available in common programming languages One of the most common is the if statement If statement has three different forms in PHP Form1 - Single Statement if (logical expression) statement; Form2 - Multiple Statements if (logical expression) { statement1; statement2; } Form3 – Multiple Statements if (logical expression): statement1; statement2; endif;
Else and else if follow the same format as the if statements if (logical expression) { statement1; statement2; } elseif (logical expression){ statement1; statement2; } else{
cs.metrostate.edu/~f itzgesu/courses/ics325/f all04/Ch01Notes.htm 8/9 8/28/12 Chapter 1 – PHP Crash Course statement1; statement2; } The Switch Statement is a handy tool for replacing multiple else-ifs switch (expression){ case expression1: statement; break; case expression2: statement; default: statement; }
NOTE: the break statement can also be used to exit out of loops and scripts
Iteration PHP support three of the most common looping structure: for, while, and do… while. While Loops Check condition, execute statements, and then loop While(logical expression) Statements; For Loops Loop a set number of times executing statements each time For (expression1; comparison; expression2) Statements; Do…While Loops execute statements, check condition, and then loop Do Statements; While (logical expression)
NOTE: Code readability. Indent your code. Use comments. Describe functions and web pages.
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