PHP and MySQL Programming/Syntax Overview

PHP tags:

<?php [code] ?>

<?php
 print "Hello World\n";
 $date = date("Y-m-d H:i:s");
 print "The date and time at the moment is $date";
 ?>

Commenting

//

echo "Hello"; // Everything from the hash is commented out

// This entire line is commented out

#

/* (text) */

 /*All of this is
 commented out.
 Even this line!*/

Variables

 $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.

$c = "response";
$$c = "Hello Ralfe"; # this assigns "Hello Ralfe" to $response.

$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.

$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:

Operators

Arithmetic Operators

$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

$a = 4;
$b = $a;
// $b = 4;

Comparison Operators

$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

$a = "Fill the halls ";
$b = "with poisoned ivy...";
$c = $a . $b; # the '.' operator concatenates two variables.
// $c = "Fill the halls with poisoned ivy...";

Arrays

$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

 $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

 $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

 for ($i = 0; $i < 10; $i++) {
 # initialize $i ; while condition ; increment statement
 echo $i;
 }
 
 // OUTPUT:
 // 0123456789

Foreach statement

 $a = array(1, 2, 3, 4, 5);
 
 foreach ($a as $val){
 echo $val;
 }
 
 // OUTPUT:
 // 12345

While statement

 while ($row = mysql_fetch_row($result)){
 print $row[0];
 }

Do ... while statement

 $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

 function square_number($number) {
 return ($number * $number);
 }
 
 $answer = square_number(10);
 echo "The answer is {$answer}";
 
 // OUTPUT:
 // The answer is 100

Classes

 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

function __construct($name)

function dog($name)