PHP 01: Introduction
Introduction to PHP.
Overview
PHP enables scripting dynamic server-side actions.
Why PHP?
Without a dynamic scripting language, a web page is entirely static, where the time is exactly as typed:
<!DOCTYPE html>
<html lang="en>
<head>
<meta charset="UTF-8">
<title>Static vs Dynamic</title>
</head>
<body>
<h1>This is Static</h1>
<p>
The time is
9:52 am
</p>
</body>
</html>
With PHP we get a dynamic web page, where the time updates continuously:
<!DOCTYPE html>
<html lang="en>
<head>
<meta charset="UTF-8">
<title>Static vs Dynamic</title>
</head>
<body>
<h1>This is Static</h1>
<p>
The time is
<?php>
echo date(DATE_RSS)
?>
</p>
</body>
</html>
PHP Basics
Comments
Use slash star for multi-line comments and double-slash for single-line comments:
/*
* A multi-line comment
* this is
*/
// A single-line comment this is
Variables
Define a php variable with the dollar symbol $:
<?php
$myVariable = 0;
?>
Insert a variable in a text string:
<?php
$galaxy = "Andromeda";
$atmosphere = "habitable";
echo "The atmosphere in the {$galaxy} star system is {$atmosphere}.";
?>
Casting
This expression returns a floating point value:
<?php
$alpha = 33;
$beta = 12;
$charlie = $alpha / $beta ;
echo $charlie;
?>
Prefix the desired format to cast the expression to return an integer:
<?php
$alpha = 33;
$beta = 12;
$charlie = $alpha / $beta ;
echo (int) $charlie;
?>
Functions
Define a php function with the keyword function:
<?php
function myFunction($myParam) {
$counter = $myParam + 1;
return $counter;
}
?>
Conditionals
Use the conditional operators:
|| // -- OR
&& // -- AND
! // -- NOT
Control of Flow
Use if, else and elseif conditional statements:
<?php
$myStr = "This is a String";
if (strtoupper($myStr) == $myStr) {
echo "UPPER CASE";
}
elseif (strtolower($myStr) == $myStr) {
echo "lower case";
}
else {
echo "Mixed Case";
}
?>
Use switch statements:
<?php
$faveColour = "purple";
switch ($faveColour) {
case "red":
echo "You like Red!";
break;
case "green":
echo "You like Green!";
break;
case "blue":
echo "You like Blue!";
break;
default:
echo "You don't like RGB!";
}
?>
Use the ternary operator as shorthand for if and else statements:
<?php
$celcius = 10;
echo $celcius <= 0 ? "stay indoors" : "go outside";
?>
Loops
A basic while loop:
<?php
$gallons = 15;
while ($gallons < 20) {
echo "Petrol is low - keep filling!";
++$gallons;
}
?>
Alternative syntax:
<?php
$gallons = 15;
while (++$gallons < 20) {
echo "Petrol is low - keep filling! <br>";
}
?>
do…while syntax:
<?php
$gallons = 15;
do {
echo "Petrol is low - keep filling! <br>";
} while (++$gallons < 20);
?>
for loop:
<?php
// times tables
$multiplier = 12;
for ($count = 1 ; $count <= 12; ++$count)
echo "$count times $multiplier is " . $count * $multiplier . "<br>";
?>
QED
© Adam Heinz
17 June 2025