Introduction to PHP
Dr. Charles Severance
www.wa4e.com
Science Calculations
System
http://en.wikipedia.org/wiki/History_of_programming_languages
System
Scripting/
Interpreted
C uses curly braces { } for code blocks.
About the PHP Language
- Curly braces, semicolons, no significant whitespace
- Dollar signs to start variable names, associative arrays
Philosophy of PHP
<h1>Hello from Dr. Chuck's HTML Page</h1>
<p>
<?php
echo "Hi there.\n";
$answer = 6 * 7;
echo "The answer is $answer, what ";
echo "was the question again?\n";
?>
</p>
<p>Yes another paragraph.</p>
<h1>Hello from Dr. Chuck's HTML Page</h1>
<p>
<?php
echo "Hi there.\n";
$answer = 6 * 7;
echo "The answer is $answer, what ";
echo "was the question again?\n";
?>
</p>
<p>Yes another paragraph.</p>
PHP from the Command Line
<?php
echo("Hello World!");
echo("\n");
?>
Basic Syntax
Keywords
http://php.net/manual/en/reserved.php
abstract and array() as break case catch class clone const continue declare default do else elseif end declare endfor endforeach endif endswitch endwhile extends final for foreach function global goto if implements interface instanceof namespace new or private protected public static switch $this throw try use var while xor
Variable Names
http://php.net/manual/en/language.variables.basics.php
$abc = 12;
$total = 0;
$largest_so_far = 0;
abc = 12;
$2php = 0;
$bad-punc = 0;
Variable Name Weirdness
Things that look like variables but are missing a dollar sign can be confusing.
$x = 2;
$y = x + 5;
print $y;
$x = 2;
y = $x + 5;
print $x;
5
Parse error
Variable Name Weirdness
Things that look like variables but are missing a dollar sign as an array index are unpredictable....
$x = 5;
$y = array("x" => "Hello");
print $y[x];
Hello
Strings / Different + Awesome
http://php.net/manual/en/language.types.string.php
<?php
echo "this is a simple string\n";
echo "You can also have embedded newlines in
strings this way as it is
okay to do";
// Outputs: This will expand:
// a newline
echo "This will expand: \na newline";
// Outputs: Variables do 12
$expand = 12;
echo "Variables do $expand\n";
Double Quote
<?php
echo 'this is a simple string';
echo 'You can also have embedded newlines in
strings this way as it is
okay to do';
// Outputs: Arnold once said: "I'll be back"
echo 'Arnold once said: "I\'ll be back"';
// Outputs: This will not expand: \n a newline
echo 'This will not expand: \n a newline';
// Outputs: Variables do not $expand $either
echo 'Variables do not $expand $either';
Single Quote
Comments in PHP ☺
http://php.net/manual/en/language.basic-syntax.comments.php
echo 'This is a test'; // This is a c++ style comment
/* This is a multi line comment
yet another line of comment */
echo 'This is yet another test';
echo 'One Final Test'; # This is a shell-style comment
Output
<?php
$x = "15" + 27;
echo $x;
echo("\n");
echo $x, "\n";
print $x;
print "\n";
print($x);
print("\n");
?>
Expressions
Expressions
<?php
$x = "15" + 27;
echo($x);
echo("\n");
?>
42
Expressions
Operators of Note
Increment / Decrement
$x = 12;
$y = 15 + $x++;
echo "x is $x and y is $y \n";
x is 13 and y is 27
Increment / Decrement
$x = 12;
$y = 15 + $x;
$x = $x + 1;
echo "x is $x and y is $y \n";
x is 13 and y is 27
String Concatenation
PHP uses the period character for concatenation, because the plus character would instruct PHP to do the best it could to add the two things together, converting if necessary.
$a = 'Hello ' . 'World!';
echo $a . "\n";
Hello World!
Ternary
The ternary operator comes from C. It allows conditional expressions. It is like a one-line if-then-else. Like all “contraction” syntaxes, we must use it carefully.
$www = 123;
$msg = $www > 100 ? "Large" : "Small" ;
echo "First: $msg \n";
$msg = ( $www % 2 == 0 ) ? "Even" : "Odd";
echo "Second: $msg \n";
$msg = ( $www % 2 ) ? "Odd" : "Even";
echo "Third: $msg \n";
First: Large
Second: Odd
Third: Odd
Side-Effect Assignment
These are pure contractions. Use them sparingly.
echo "\n";
$out = "Hello";
$out = $out . " ";
$out .= "World!";
$out .= "\n";
echo $out;
$count = 0;
$count += 1;
echo "Count: $count\n";
Hello World!
Count: 1
Conversion / Casting
As PHP evaluates expressions, sometimes values in the expression need to be converted from one type to another as the computations are done.
Casting
$a = 56; $b = 12;
$c = $a / $b;
echo "C: $c\n";
$d = "100" + 36.25 + TRUE;
echo "D: ". $d . "\n";
echo "D2: ". (string) $d . "\n";
$e = (int) 9.9 - 1;
echo "E: $e\n";
$f = "sam" + 25;
echo "F: $f\n";
$g = "sam" . 25;
echo "G: $g\n";
C: 4.66666666667
D: 137.25
D2: 137.25
E: 8
F: 25
G: sam25
In PHP, division forces operands to be floating point. PHP converts expression values silently and aggressively.
PHP vs. Python
$x = "100" + 25;
echo "X: $x\n";
$y = "100" . 25;
echo "Y: $y\n";
$z = "sam" + 25;
echo "Z: $z\n";
X: 125
Y: 10025
Z: 25
x = int("100") + 25
print "X:", x
y = "100" + str(25)
print "Y:", y
z = int("sam") + 25
print "Z:", z
X: 125
Y: 10025
Traceback:"cast.py", line 5
z = int("sam") + 25;
ValueError: invalid literal
Casting
echo "A".FALSE."B\n";
echo "X".TRUE."Y\n";
AB
X1Y
The concatenation operator tries to convert its operands to strings.
TRUE becomes an integer 1 and then becomes a string. FALSE is “not there” - it is even “smaller” than zero, at least when it comes to width.
Equality versus Identity
The equality operator (==) in PHP is far more aggressive than in most other languages when it comes to data conversion during expression evaluation.
if ( 123 == "123" ) print ("Equality 1\n");
if ( 123 == "100"+23 ) print ("Equality 2\n");
if ( FALSE == "0" ) print ("Equality 3\n");
if ( (5 < 6) == "2"-"1" ) print ("Equality 4\n");
if ( (5 < 6) === TRUE ) print ("Equality 5\n");
http://php.net/manual/en/function.strpos.php
$vv = "Hello World!";
echo "First:" . strpos($vv, "Wo") . "\n";
echo "Second: " . strpos($vv, "He") . "\n";
echo "Third: " . strpos($vv, "ZZ") . "\n";
if (strpos($vv, "He") == FALSE ) echo "Wrong A\n";
if (strpos($vv, "ZZ") == FALSE ) echo "Right B\n";
if (strpos($vv, "He") !== FALSE ) echo "Right C\n";
if (strpos($vv, "ZZ") === FALSE ) echo "Right D\n";
print_r(FALSE); print FALSE;
echo "Where were they?\n";
First:6
Second: 0
Third:
Wrong A
Right B
Right C
Right D
Where were they?
Beware FALSE variables. They are detectable but not visible...
Control Structures
Conditional - if
<?php
$ans = 42;
if ( $ans == 42 ) {
print "Hello world!\n";
} else {
print "Wrong answer\n";
}
?>
Hello World!
Whitespace Does Not Matter
<?php
$ans = 42;
if ( $ans == 42 ) {
print "Hello world!\n";
} else {
print "Wrong answer\n";
}
?>
<?php $ans = 42; if ( $ans == 42 ) { print
"Hello world!\n"; } else { print "Wrong answer\n"; }
?>
Which Style do You Prefer?
<?php
$ans = 42;
if ( $ans == 42 )
{
print "Hello world!\n";
}
else
{
print "Wrong answer\n";
}
?>
<?php
$ans = 42;
if ( $ans == 42 ) {
print "Hello world!\n";
} else {
print "Wrong answer\n";
}
?>
Aesthetics
Multi-way
$x = 7;
if ( $x < 2 ) {
print "Small\n";
} elseif ( $x < 10 ) {
print "Medium\n";
} else {
print "LARGE\n";
}
print "All done\n";
x < 2
print 'Small'
yes
no
print 'All Done'
x<10
print 'Medium'
yes
print 'LARGE'
no
Curly Braces are Not Required
if ($page == "Home") echo "You selected Home";
elseif ($page == "About") echo "You selected About";
elseif ($page == "News") echo "You selected News";
elseif ($page == "Login") echo "You selected Login";
elseif ($page == "Links") echo "You selected Links";
if ($page == "Home") { echo "You selected Home"; }
elseif ($page == "About") { echo "You selected About"; }
elseif ($page == "News") { echo "You selected News"; }
elseif ($page == "Login") { echo "You selected Login"; }
elseif ($page == "Links") { echo "You selected Links"; }
$fuel = 10;
while ($fuel > 1) {
print "Vroom vroom\n";
}
$fuel = 10;
while ($fuel > 1) {
print "Vroom vroom\n";
$fuel = $fuel - 1;
}
A while loop is a “zero-trip” loop with the test at the top before the first iteration starts. We hand construct the iteration variable to implement a counted loop.
$count = 1;
do {
echo "$count times 5 is " . $count * 5;
echo "\n";
} while (++$count <= 5);
1 times 5 is 5
2 times 5 is 10
3 times 5 is 15
4 times 5 is 20
5 times 5 is 25
A do-while loop is a “one-trip” loop with the test at the bottom after the first iteration completes.
for($count=1; $count<=6; $count++ ) {
echo "$count times 6 is " . $count * 6;
echo "\n";
}
A for loop is the simplest way to construct a counted loop.
1 times 6 is 6
2 times 6 is 12
3 times 6 is 18
4 times 6 is 24
5 times 6 is 30
6 times 6 is 36
for($count=1; $count<=6; $count++ ) {
echo "$count times 6 is " . $count * 6;
echo "\n";
}
1 times 6 is 6
2 times 6 is 12
3 times 6 is 18
4 times 6 is 24
5 times 6 is 30
6 times 6 is 36
A for loop is the simplest way to construct a counted loop.
Before loop starts
Loop runs while TRUE (top-test)
Run after each iteration.
Breaking Out of a Loop
for($count=1; $count<=600; $count++ ) {
if ( $count == 5 ) break;
echo "Count: $count\n";
}
echo "Done\n";
Count: 1
Count: 2
Count: 3
Count: 4
Done
Finishing an Iteration with continue
The continue statement ends the current iteration. jumps to the top of the loop, and starts the next iteration.
for($count=1; $count<=10; $count++ ) {
if ( ($count % 2) == 0 ) continue;
echo "Count: $count\n";
}
echo "Done\n";
Count: 1
Count: 3
Count: 5
Count: 7
Count: 9
Done
Summary
This is a sprint through some of the unique language features of PHP.
Acknowledgements / Contributions
These slides are Copyright 2010- Charles R. Severance (www.dr-chuck.com) as part of www.wa4e.com and made available under a Creative Commons Attribution 4.0 License. Please maintain this last slide in all copies of the document to comply with the attribution requirements of the license. If you make a change, feel free to add your name and organization to the list of contributors on this page as you republish the materials.
Initial Development: Charles Severance, University of Michigan School of Information
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