< PHP and MySQL Programming
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. [1]
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