Expressions andControl Flow

Expressions

• An expression is a combination of values, variables, operators, and functions that results in a value

y = 3(abs(2x) + 4)

• which in PHP would be: $y = 3 * (abs(2*$x) + 4);

Boolian

• Example 4.1

• <?php• echo "a: [" . (20 > 9) . "]<br />";• echo "b: [" . (5 == 6) . "]<br />";• echo "c: [" . (1 == 0) . "]<br />";• echo "d: [" . (1 == 1) . "]<br />";• ?>

Literals and Variables

• Example 4-3. Five types of literals • <?php

$myname = "Brian"; $myage = 37;echo "a: " . 73echo "b: " . "Hello" echo "c: " . FALSE echo "d: " . $myname echo "e: " . $myage ?>

. "<br />"; // Numeric literal

. "<br />"; // String literal

. "<br />"; // Constant literal

. "<br />"; // Variable string literal . "<br />"; // Variable numeric literal

Expression Statement

• Example 4-4. An expression and a statement • <?php

$days_to_new_year = 366 - $day_number; // Expression if ($days_to_new_year < 30){

• echo "Not long now till new year"; // Statement } • ?>

Operators

• Table 4-1. PHP operator types • Operator Description Example • Arithmetic Array Assignment Bitwise • Basic mathematics

Array unionAssign valuesManipulate bits within bytes

• $a + $b $a + $b $a = $b + 23 12 ^ 9

PHP operator types

• Table 4-1. PHP operator types • Operator Description Example • Arithmetic Array Assignment Bitwise • Basic mathematics

Array unionAssign valuesManipulate bits within bytes

• $a + $b $a + $b $a = $b + 23 12 ^ 9

Operator Precedence

• If all operators had the same precedence, they would be processed in the order in which they are encountered. In fact, many operators do have the same precedence, so let’s look at a few in Example 4-5.

• Example 4-5. Three equivalent expressions • 1 +2+3-4+5• 2 -4+5+3+1 • 5 +2-4+1+3

Operators

• PHP’s operators in order of precedence from high to low. • Table 4-2. The precedence of PHP operators (high to

low)

Operators cont

Associativity

Relational Operators

• the equality operator is == (two equals signs)• Example 4-12. Assigning a value and testing for equality

<?php$month = "March";if ($month == "March") echo "It's springtime";?>

• Returning either TRUE or FALSE, the equality operator enables you to test for conditions using, for example, an if statement

Comparison operators

• you can test for more than just equality and inequality. PHP also gives you > (is greater than), < (is less than), >= (is greater than or equal to), and <= (is less than or equal to)

• Example 4-15. The four comparison operators• <?php• $a = 2; $b = 3;• if ($a > $b) echo "$a is greater than $b<br />";• if ($a < $b) echo "$a is less than $b<br />";• if ($a >= $b) echo "$a is greater than or equal to $b<br />";• if ($a <= $b) echo "$a is less than or equal to $b<br />";• ?>

Logical operators

Conditionals

Conditionals

• The if Statement

• The else Statement

• The elseif Statement

• The switch Statement

Conditionals

Conditional Switch Statement

The ? Operator

• Example 4-26. Using the ? operator<?phpecho $fuel <= 1 ? "Fill tank now" : "There's enough

fuel";?>

Looping

Loopie

• do...while Loops• for Loops• Breaking Out of a Loop• The continue Statement

Implicit and Explicit Casting

PHP Dynamic Linking

• You can split your website up into sensible sections of PHP code, each one self-contained, and therefore treat yourself to a much easier future developing each new feature and maintaining old ones

• Dynamic Linking in Action Wordpress