PHP and MySQL Programming/PHP Syntax

PHP tags:

<?php [code] ?>

• Enclose php code

• Can be configured in the php.ini to be <? ?>, <script language="php"> </script> etc.

• 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”;
?>

<?=

• Used if you just want to print out the value of a variable

Example:

<?php
$name = "Bobby";
?>

<?=$name?>

Which will output Bobby.

Example:

<?=date(“Y-m-d H:i:s”)?> 

Which will output something like 2005-11-09 19:40:05.

Commenting

#

• Comments out one line

• Example:

echo “Hello”; # Everything from the hash is commented out

• Example:

# This entire line is commented out

//

• Works just as in Java and JavaScript

• 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.

e.g. : $a = “Hello World”; # this assigns the string “Hello World” to $a.

e.g. : $b = “$a, I'm Ralfe”; # this assigns “Hello World, I'm Ralfe” to $b.

e.g. : $b = $a.”, I'm Ralfe”; # exactly the same as the previous example.

➢ PHP supports dynamic variables.

e.g. : $c = “response”;

e.g. : $$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.

e.g. : $a = 4;

e.g. : $b = 12;

e.g. : print “The value of a is $a.”; # Uses a as a String.

e.g. : $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.

e.g. : $a = true;

e.g. : $b = 1;

e.g. : # $a and $b are the same thing!

e.g. : $c = false;

e.g. : $d = 0;

e.g. : # $c and $d are the same thing!

Operators

➢ Arithmetic Operators

$a = 4;

$b = 2;

// Addition: $a + $b = 6

// Subtraction: $a - $b = 2

// Multiplication: $a * $b = 8

// Division: $a / $b = 2

// Modulus: $a % $b = 0

// Increment: $a++

// Decrement: $a--

➢ 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 not equal

$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

PHP supports both numerically indexed arrays as well as associative 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 THEN 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 dog($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