PHP and MySQL Programming/Syntax Overview

PHP tags: <?php [code] ?> Enclose PHP code Embedded in normal HTML code Within PHP tags, statements are separated by a ; (generally also followed by a new line). Example: <?php print "Hello World\n"; $date = date("Y-m-d H:i:s"); print "The date and time at the moment is $date"; ?> Commenting // Comments out one line Example: echo "Hello"; // Everything from the hash is commented out Example: // This entire line is commented out # Same function as // /* (text) */ Comments out everything between the /* and the */ Example: /*All of this is commented out. Even this line!*/ Variables Variables in PHP are denoted by the $ prefix. Example: $a = "Hello World"; # this assigns the string "Hello World" to $a. $b = "$a, I'm Ralfe"; # this assigns "Hello World, I'm Ralfe" to $b. $b = $a.", I'm Ralfe"; # exactly the same as the previous example. PHP supports dynamic variables. Example: $c = “response”; $$c = “Hello Ralfe”; # this assigns “Hello Ralfe” to $response. PHP variables do not have to be declared ahead of time, nor do they require a type definition. PHP handles all data type conversions. Example: $a = 4; $b = 12; print “The value of a is $a.”; # Uses a as a String. $c = $a + $b; # $a is now used as an Integer again. PHP supports Boolean variables, which can be assigned either a one or a zero, or a true or false. Example: $a = true; $b = 1; # $a and $b are equal, though not identical. $c = false; $d = 0; # $c and $d are equal, though not identical. Helpful Definitions: Equal vs Identical Equal values are equal in value, but may be of differing types. Uses == comparison operator. E.g. false is equal to 0. Identical values are equal in value and of the same type. Uses === comparison operator. E.g. false is identical only to false, it is not identical to 0. Operators Arithmetic Operators Example: $a = 4; $b = 2; $a + $b = 6; // Addition $a - $b = 2; // Subtraction $a * $b = 8; // Multiplication $a / $b = 2; // Division $a % $b = 0; // Modulus $a++; // Increment $a--; // Decrement Assignment Operators Example: $a = 4; $b = $a; // $b = 4; Comparison Operators Example: $a == $b // test if two values are equal $a === $b // test if two values are identical $a != $b // test if two values are not equal $a !== $b // test if two values are not identical $a < $b // test if the first value is less than the second $a > $b // test if the first value is greater than the second $a <= $b // test if the first value is less than or equal to the second $a >= $b // test if the first value is greater than or equal to the second Concatenation Example: $a = "Fill the halls "; $b = "with poisoned ivy..."; $c = $a . $b; # the '.' operator concatenates two variables. // $c = "Fill the halls with poisoned ivy..."; Arrays PHP supports both numerically indexed arrays as well as associative arrays. Example: $a = array(1, 2, 3, 4); // $a[0] = 1; // $a[1] = 2; // $a[2] = 3; // $a[3] = 4; $b = array("name" => "Fred", "age" => 30); // $b['name'] = "Fred"; // $b['age'] = 30; Decision and Loop Statements If ... else statement Example: $a = 1; $b = 10; if ($a > $b) { echo "a is greater than b"; } else if ($a == $b) { echo "a is equal to b"; } else { echo "a is not greater than b"; } // OUTPUT: // a is not greater than b Switch statement Example: $a = 100; switch($a) { case(10): echo "The value is 10"; break; case(100): echo "The value is 100"; break; case(1000): echo "The value is 1000"; break; default: echo "Are you sure you entered in a valid number?"; } // OUTPUT: // The value is 100 For statement Example: for ($i = 0; $i < 10; $i++) { # initialize $i ; while condition ; increment statement echo $i; } // OUTPUT: // 0123456789 Foreach statement Example: $a = array(1, 2, 3, 4, 5); foreach ($a as $val){ echo $val; } // OUTPUT: // 12345 While statement Example: while ($row = mysql_fetch_row($result)){ print $row[0]; } Do ... while statement Example: $i = 0; # Note that it might seem that $i will do{ # never be printed to the screen, but print $i; # a DO WHILE loop always executes at } while ($i >0); # least once! Functions Example: function square_number($number) { return ($number * $number); } $answer = square_number(10); echo "The answer is {$answer}"; // OUTPUT: // The answer is 100 Classes Example: class dog { var $name; function __construct($name){ $this->name = $name; } function bark(){ echo "Woof! Woof!"; } function who_am_i() { echo "My name is {$this->name}, and I am a dog"; } } $the_dog = new dog("John"); $the_dog->who_am_i(); // OUTPUT: // My name is John, and I am a dog As of PHP 5.3.3, functions with the same name as the class will no longer act as a constructor. Versions prior to 5.3.3 the function __construct($name) line could be replaced with function dog($name) to achieve the same effect. http://php.net/manual/en/language.oop5.decon.php