Expressions and Control Flow An expression is a

Expressions and Control Flow

• An expression is a combination of values, variables, operators, and functions that results in a value y = 3(abs(2 x) + 4) • which in PHP would be: $y = 3 * (abs(2*$x) + 4); Expressions

• Example 4 -3. Five types of literals • <? php $myname = "Brian"; $myage = 37; echo "a: ". 73 echo "b: ". "Hello" echo "c: ". FALSE echo "d: ". $myname echo "e: ". $myage ? >. " "; // Numeric literal. " "; // String literal. " "; // Constant literal. " "; // Variable string literal. " "; // Variable numeric literal Literals and Variables

• 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

• • 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 + 23 12 ^ 9 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 + 23 12 ^ 9 PHP operator types

• 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

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

Operators cont

Associativity

• 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

• 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 $b "; • if ($a < $b) echo "$a is less than $b "; • if ($a >= $b) echo "$a is greater than or equal to $b "; • if ($a <= $b) echo "$a is less than or equal to $b "; • ? > Comparison operators

Logical operators

Conditionals

• The if Statement • The elseif Statement • The switch Statement Conditionals

Conditionals

Conditional Switch Statement

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

Looping

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

Implicit and Explicit Casting

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