PHP else statement
A PHP else statement can follow an if
block. If the condition of the if
does not evaluate to TRUE
, the code block following else
will be executed.
$condition = FALSE;
if ($condition) {
// This code block will not execute
} else {
// This code block will execute
}
PHP comparison operators
PHP comparison operators are used to compare two values and return TRUE
or FALSE
depending on the validity of the comparison. Comparison operators include:
- identical (
===
) - not identical (
!==
) - greater than (
>
) - less than (
<
) - greater than or equal (
>=
) - less than or equal (
<=
)
// Comparison operators
1 > 3; // FALSE
3 > 1; // TRUE
250 >= 250; // TRUE
1 === 1; // TRUE
1 === 2; // FALSE
1 === "1"; // FALSE
PHP If Statements
PHP if
statements evaluate a boolean value or expression and execute the provided code block if the expression evaluates to TRUE
.
if (TRUE){
echo "TRUE is always true";
}
$condition1 = TRUE;
if ($condition1) {
// This code block will execute
}
$condition2 = FALSE;
if ($condition2) {
// This code block will not execute
}
PHP switch statement
PHP switch
statements provide a clear syntax for a series of comparisons in which a value or expression is compared to many possible matches and code blocks are executed based on the matching case
.
In PHP, once a matched case
is encountered, the code blocks of all subsequent cases (regardless of match) will be executed until a return
, break
, or the end of the statement is reached. This is known as fall through.
switch ($letter_grade){
case "A":
echo "Terrific";
break;
case "B":
echo "Good";
break;
case "C":
echo "Fair";
break;
case "D":
echo "Needs Improvement";
break;
case "F":
echo "See me!";
break;
default:
echo "Invalid grade";
}
PHP readline()
The PHP built-in readline()
function takes a string with which to prompt the user. It waits for the user to enter text into the terminal and returns that value as a string.
echo "\nWhat's your name?\n";
$name = readline(">> "); // receives user input
PHP elseif statements
PHP elseif
statements must be paired with an if
statement, but many elseif
s can be chained from a single if
.
elseif
s provide an additional condition to check (and corresponding code to execute) if the conditional statements of the if
block and any preceding elseif
s are not met.
$fav_fruit = "orange";
if ($fav_fruit === "banana"){
echo "Enjoy the banana!";
} elseif ($fav_fruit === "apple"){
echo "Enjoy the apple!";
} elseif ($fav_fruit === "orange"){
echo "Enjoy the orange!";
} else {
echo "Enjoy the fruit!";
}
// Prints: Enjoy the orange!
PHP Truthy and Falsy
PHP values within a condition will always be evaluated to TRUE
or FALSE
. Values that will evaluate to TRUE
are known as truthy and values that evaluate to FALSE
are known as falsy.
Falsy values include:
false
0
- empty strings
null
undefined
NaN
.
All other values are truthy.
if ("What's going on?"){ // evaluates to TRUE
echo "Let us explain…";
}
// Prints: Let us explain…
PHP Boolean Values
PHP Boolean values are either TRUE
or FALSE
, which are the only members of the boolean
type
// booleans
$is_true = TRUE;
$is_false = FALSE;
echo gettype($is_true);
// Prints: boolean
echo gettype($is_false);
// Prints: boolean
PHP ternary operator
In PHP, the ternary operator allows for a compact syntax in the case of binary (if/else
) decisions. It evaluates a single condition and executes one expression and returns its value if the condition is met and the second expression otherwise.
The syntax for the ternary operator looks like the following:
condition ? expression1 : expression2
// Without ternary
$isClicked = FALSE;
if ($isClicked) {
$link_color = "purple";
} else {
$link_color = "blue";
}
// $link_color = "blue";
// With ternary
$isClicked = FALSE;
$link_color = $isClicked ? "purple" : "blue";
// $link_color = "blue";
PHP Nested Conditionals
In PHP, nested conditional statements deepen the complexity of our programs’ decision-making capabilities. They allow us to create programs where each decision made sends our program on a different route where it might encounter additional decisions.
$num = 5;
// nested conditional
if ($num > 0){
echo 'The number is positive. <br>';
if ($num % 2 === 0){
echo 'The number is even.';
}
} else {
echo 'The number is negative.';
}
PHP Logical Operators
In PHP, expressions that use logical operators evaluate to boolean values. Logical operators include:
- or (
||
) - and (
&&
) - exclusive or (
xor
) - not (
!
)
// Examples of Logical Operators:
TRUE || TRUE; // Evaluates to: TRUE
FALSE || TRUE; // Evaluates to: TRUE
TRUE && TRUE; // Evaluates to: TRUE
FALSE && TRUE; // Evaluates to: FALSE
!TRUE; // Evaluates to: FALSE
!FALSE; // Evaluates to: TRUE
TRUE xor TRUE; // Evaluates to: FALSE
FALSE xor TRUE; // Evaluates to: TRUE
PHP && Operator
The logical operator &&
returns:
TRUE
only if both of its operands evaluate to true.FALSE
if either or both of its operands evaluate to false.
TRUE && TRUE; // Evaluates to: TRUE
FALSE && TRUE; // Evaluates to: FALSE
TRUE && FALSE; // Evaluates to: FALSE
FALSE && FALSE; // Evaluates to: FALSE
$passingGrades = TRUE;
$extracurriculars = TRUE;
if ($passingGrades && $extracurriculars){
echo "You meet the graduation requirements.";
}
// Prints: You meet the graduation requirements.
PHP ! (not) Operator
In PHP, the not operator (!
) is used to invert a Boolean value or expression.
!TRUE; // Evaluates to: FALSE
!FALSE; // Evaluates to: TRUE
PHP Operator Precedence
Each operator in PHP holds a different operator precedence.
We can avoid operator precedence confusion by using parentheses for force the evaluation we want.
TRUE || TRUE && FALSE // Evaluates to: TRUE
(TRUE || TRUE) && FALSE // Evaluates to: FALSE
PHP Xor Operator
In PHP, the logical operator xor
stands for exclusive or.
It takes two different boolean values or expressions as its operands and returns a single boolean value.
xor
evaluates to TRUE
only if either its left operand or its right operand evaluate to TRUE
, but not both.
TRUE xor TRUE; // Evaluates to: FALSE
FALSE xor TRUE; // Evaluates to: TRUE
TRUE xor FALSE; // Evaluates to: TRUE
FALSE xor FALSE; // Evaluates to: FALSE
Logical Operators - Alternate Syntax
PHP provides an alternate syntax for the ||
operator — the or
operator.
It also provides an alternate syntax for &&
operator — the and
operator.
These operators have the advantage of making our code more human readable.
// The or Operator:
TRUE or TRUE; // Evaluates to: TRUE
FALSE or TRUE; // Evaluates to: TRUE
TRUE or FALSE; // Evaluates to: TRUE
FALSE or FALSE; // Evaluates to: FALSE
// The and Operator:
TRUE and TRUE; // Evaluates to: TRUE
FALSE and TRUE; // Evaluates to: FALSE
TRUE and FALSE; // Evaluates to: FALSE
FALSE and FALSE; // Evaluates to: FALSE
Multi-File Programs: include
A way to improve our code and separate concerns is with modularity, separating a program into distinct, manageable chunks where each provides a piece of the overall functionality. Instead of having an entire program located in a single file, code is organized into separate files.
In PHP, files can be included in another file with the keyword include
. An include statement is followed by a string with a path to the file to be included. The code from the file will be executed.
// one.php
echo "How are";
// two.php
echo " you?";
// index.php
echo "Hello! ";
include "one.php";
include "two.php";
// Prints: Hello! How are you?