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Expressions and Control Flow

Expressions and Control Flow. 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);. Expressions. Example 4.1 < ? php echo "a: [" . (20 > 9) . "]< br />";

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Expressions and Control Flow

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  1. Expressions andControl Flow

  2. 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); Expressions

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

  4. 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 Literals and Variables

  5. 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 } • ?> Expression Statement

  6. Table 4-1. PHP operator types • Operator Description Example • Arithmetic Array Assignment Bitwise • Basic mathematicsArray unionAssign valuesManipulate bits within bytes • $a + $b $a + $b $a = $b + 23 12 ^ 9 Operators

  7. Table 4-1. PHP operator types • Operator Description Example • Arithmetic Array Assignment Bitwise • Basic mathematicsArray unionAssign valuesManipulate bits within bytes • $a + $b $a + $b $a = $b + 23 12 ^ 9 PHP operator types

  8. 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 Operator Precedence

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

  10. Operators cont

  11. Associativity

  12. 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 Relational Operators

  13. 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 />"; • ?> Comparison operators

  14. Logical operators

  15. Conditionals

  16. The if Statement • The else Statement • The elseifStatement • The switch Statement Conditionals

  17. Conditionals

  18. Conditional Switch Statement

  19. Example 4-26. Using the ? operator <?php echo $fuel <= 1 ? "Filltanknow" : "There'senough fuel"; ?> The ? Operator

  20. Looping

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

  22. Implicit and Explicit Casting

  23. 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 PHP DynamicLinking

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