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:

<?phpprint"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=“HelloRalfe”;# 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“Thevalueofais$a.”;# Uses a as a String.$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";}elseif($a==$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 $i ; while condition ; increment statementecho$i;}// OUTPUT:// 0123456789

Foreach statement

Example:

$a=array(1,2,3,4,5);foreach($aas$val){echo$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 $i willdo{# never be printed to the screen, butprint$i;# a DO WHILE loop always executes at}while($i>0);# least once!

Functions

Example:

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

Classes

Example:

classdog{var$name;function__construct($name){$this->name=$name;}functionbark(){echo"Woof! Woof!";}functionwho_am_i(){echo"My name is {$this->name}, and I am a dog";}}$the_dog=newdog("John");$the_dog->who_am_i();// OUTPUT:// My name is John, and I am a dog