1. Expressions and Control Flow

2. 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);

3. Boolian Example 4.1 <?php echo "a: [". (20 > 9). "] "; echo "b: [". (5 == 6). "] "; echo "c: [". (1 == 0). "] "; echo "d: [". (1 == 1). "] "; ?>

4. Literals and Variables Example 4-3. Five types of literals. " "; // Numeric literal. " "; // String literal. " "; // Constant literal. " "; // Variable string literal. " "; // Variable numeric literal

5. 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 } ?>

6. Operators Table 4-1. PHP operator types Operator Description Example Arithmetic Array Assignment Bitwise Basic mathematics Array union Assign values Manipulate bits within bytes $a + $b $a + $b $a = $b + 23 12 ^ 9

7. PHP operator types Table 4-1. PHP operator types Operator Description Example Arithmetic Array Assignment Bitwise Basic mathematics Array union Assign values Manipulate bits within bytes $a + $b $a + $b $a = $b + 23 12 ^ 9

8. 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

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

10. Operators cont

11. Associativity

12. 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

13. Comparison operators you can test for more than just equality and inequality. PHP also gives you > (is greater 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 $b "; if ($a "; if ($a >= $b) echo "$a is greater than or equal to $b "; if ($a "; ?>

14. Logical operators

15. Conditionals

16. The if Statement The else Statement The elseif Statement The switch Statement

17. Conditionals

18. Conditional Switch Statement

19. The ? Operator Example 4-26. Using the ? operator <?php echo $fuel <= 1 ? "Fill tank now" : "There's enough fuel"; ?>

20. Looping

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

22. Implicit and Explicit Casting

23. 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