PHP Conditional Statements
In programming, we often need our code to make decisions based on certain conditions. PHP provides several conditional statements that allow you to execute different blocks of code depending on whether specified conditions are true or false.
What Are Conditional Statements?
Conditional statements are control structures that enable your program to take different paths based on whether a specified condition evaluates to true or false. They're like forks in the road that determine which way your code will go.
The if Statement
The if statement is the most basic conditional statement. It executes a block of code only if the specified condition evaluates to true.
Syntax
if (condition) {
// Code to execute if condition is true
}
Example
<?php
$temperature = 30;
if ($temperature > 25) {
echo "It's a hot day!";
}
?>
Output:
It's a hot day!
In this example, the message "It's a hot day!" is displayed because the condition $temperature > 25 evaluates to true.
The if...else Statement
The if...else statement allows you to execute one block of code if the condition is true and another block if it's false.
Syntax
if (condition) {
// Code to execute if condition is true
} else {
// Code to execute if condition is false
}
Example
<?php
$temperature = 20;
if ($temperature > 25) {
echo "It's a hot day!";
} else {
echo "It's not that hot today.";
}
?>
Output:
It's not that hot today.
Since the temperature is 20, which is not greater than 25, the condition evaluates to false, and the code in the else block is executed.
The if...elseif...else Statement
When you need to check multiple conditions, the if...elseif...else statement comes in handy.
Syntax
if (condition1) {
// Code to execute if condition1 is true
} elseif (condition2) {
// Code to execute if condition1 is false and condition2 is true
} else {
// Code to execute if all conditions are false
}
Example
<?php
$temperature = 15;
if ($temperature > 25) {
echo "It's a hot day!";
} elseif ($temperature >= 15 && $temperature <= 25) {
echo "It's a pleasant day!";
} else {
echo "It's a cold day!";
}
?>
Output:
It's a pleasant day!
In this example, since the temperature is 15, the second condition evaluates to true, and "It's a pleasant day!" is displayed.
Nested if Statements
You can place if statements inside other if statements to create more complex conditional logic.
Example
<?php
$temperature = 30;
$isRaining = false;
if ($temperature > 25) {
echo "It's a hot day! ";
if ($isRaining) {
echo "But it's raining, so it feels cooler.";
} else {
echo "And there's no rain to cool things down.";
}
}
?>
Output:
It's a hot day! And there's no rain to cool things down.
The switch Statement
The switch statement is an alternative to using multiple if...elseif statements when you want to compare a single variable against multiple possible values.
Syntax
switch (expression) {
case value1:
// Code to execute if expression equals value1
break;
case value2:
// Code to execute if expression equals value2
break;
// ... more cases ...
default:
// Code to execute if expression doesn't match any case
}
Example
<?php
$dayOfWeek = 3;
switch ($dayOfWeek) {
case 1:
echo "Today is Monday";
break;
case 2:
echo "Today is Tuesday";
break;
case 3:
echo "Today is Wednesday";
break;
case 4:
echo "Today is Thursday";
break;
case 5:
echo "Today is Friday";
break;
case 6:
echo "Today is Saturday";
break;
case 7:
echo "Today is Sunday";
break;
default:
echo "Invalid day number";
}
?>
Output:
Today is Wednesday
Since $dayOfWeek is 3, the third case is matched, and "Today is Wednesday" is displayed.
Important Notes About switch Statements
- The
breakstatement is crucial - without it, the code will continue executing the following cases, even if they don't match. - The
defaultcase is optional but recommended for handling unexpected values. - You can have multiple cases execute the same code by stacking them:
<?php
$dayOfWeek = 6;
switch ($dayOfWeek) {
case 1:
case 2:
case 3:
case 4:
case 5:
echo "It's a weekday";
break;
case 6:
case 7:
echo "It's the weekend";
break;
default:
echo "Invalid day number";
}
?>
Output:
It's the weekend
The Ternary Operator
The ternary operator is a shorthand way to write simple if...else statements. It's useful when you want to assign a value based on a condition.
Syntax
(condition) ? value_if_true : value_if_false;
Example
<?php
$temperature = 30;
$weather = ($temperature > 25) ? "hot" : "not hot";
echo "The weather is " . $weather;
?>
Output:
The weather is hot
This is equivalent to:
<?php
$temperature = 30;
if ($temperature > 25) {
$weather = "hot";
} else {
$weather = "not hot";
}
echo "The weather is " . $weather;
?>
Null Coalescing Operator (??)
Introduced in PHP 7, the null coalescing operator is a shorthand way to assign a default value if a variable is null or doesn't exist.
Syntax
$value = $possible_null ?? $default_value;
Example
<?php
// Imagine $user_preference might be set from a form or database
$user_preference = null;
$theme = $user_preference ?? "default";
echo "Using theme: " . $theme;
?>
Output:
Using theme: default
Since $user_preference is null, the value "default" is assigned to $theme.
Real-World Applications
Form Validation
<?php
// Simulating form submission
$username = "john_doe";
$password = "";
if (empty($username)) {
echo "Username is required";
} elseif (empty($password)) {
echo "Password is required";
} else {
echo "Form validation passed";
}
?>
Output:
Password is required
User Authentication
<?php
// Simulating user credentials
$stored_username = "admin";
$stored_password = "secret123";
// Simulating user input
$input_username = "admin";
$input_password = "secret123";
if ($input_username === $stored_username && $input_password === $stored_password) {
echo "Authentication successful. Welcome, " . $input_username . "!";
} else {
echo "Invalid username or password.";
}
?>
Output:
Authentication successful. Welcome, admin!
Shopping Cart Discount
<?php
$cart_total = 120;
$discount = 0;
if ($cart_total >= 200) {
$discount = 20; // 20% discount
} elseif ($cart_total >= 100) {
$discount = 10; // 10% discount
} elseif ($cart_total >= 50) {
$discount = 5; // 5% discount
}
$final_price = $cart_total - ($cart_total * $discount / 100);
echo "Original price: $" . $cart_total . "<br>";
echo "Discount applied: " . $discount . "%<br>";
echo "Final price: $" . $final_price;
?>
Output:
Original price: $120
Discount applied: 10%
Final price: $108
Summary
Conditional statements are essential tools in programming that allow your code to make decisions based on different conditions. In PHP, you have several options:
if- Executes code if a condition is trueif...else- Executes one block if a condition is true, another if it's falseif...elseif...else- Checks multiple conditions sequentiallyswitch- Compares a single variable against multiple possible values- Ternary operator - A shorthand for simple if-else statements
- Null coalescing operator - A shorthand for providing default values
Mastering conditional statements is crucial for creating dynamic, responsive PHP applications that can adapt to different scenarios and user inputs.
Exercises
-
Write a PHP script that grades a student based on their score:
- 90-100: A
- 80-89: B
- 70-79: C
- 60-69: D
- Below 60: F
-
Create a PHP program that determines whether a year is a leap year or not.
-
Build a simple calculator that performs different operations (addition, subtraction, multiplication, division) based on user input.
Additional Resources
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