Expressions and Control Flow. Expressions An expression is a combination of values, variables,...
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Transcript of Expressions and Control Flow. Expressions An expression is a combination of values, variables,...
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