Expressions and Control 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). "] "; echo "b: [". (5 == 6). "] "; echo "c: [". (1 == 0). "] "; echo "d: [". (1 == 1). "] "; ?>

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

Expression Statement Example 4-4. An expression and a statement <?php $days_to_new_year = $day_number; // Expression if ($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 union Assign values Manipulate bits within bytes $a + $b $a + $b $a = $b ^ 9

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 ^ 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

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 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 greater than or equal to), and <= (is less than or equal to) Example 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 "; ?>

Logical operators

Conditionals

The if Statement The else Statement The elseif Statement The switch Statement

Conditionals

Conditional Switch Statement

The ? Operator Example Using the ? operator <?php echo $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

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