In PHP, isset() and empty() are two commonly used functions to check the status of variables. These functions are particularly useful when you want to validate user input, check if a variable has been set, or if a variable holds a value that can be considered “empty.”

1. isset() Function

What is isset()?

• The isset() function checks if a variable is set and is not NULL.
• It returns true if the variable exists and is not NULL, otherwise it returns false.

Syntax:

isset($variable);

Example 1: Checking if a Variable is Set

$name = "John";

if (isset($name)) {
    echo "The variable 'name' is set.";
} else {
    echo "The variable 'name' is not set.";
}

Output:

The variable 'name' is set.

Example 2: Checking Multiple Variables

You can also check multiple variables at once using isset():

$name = "John";
$age = 30;

if (isset($name, $age)) {
    echo "Both 'name' and 'age' are set.";
} else {
    echo "One or both variables are not set.";
}

Output:

Both 'name' and 'age' are set.

Example 3: Unset Variables

$name = "John";
unset($name); // Unset the variable

if (isset($name)) {
    echo "The variable 'name' is set.";
} else {
    echo "The variable 'name' is not set.";
}

Output:

The variable 'name' is not set.

2. empty() Function

What is empty()?

• The empty() function checks whether a variable is empty.
• It returns true if the variable does not exist, or if its value equals false when evaluated. This includes 0, "0", "", NULL, false, an empty array [], and an unset variable.

Syntax:

empty($variable);

Example 1: Checking if a Variable is Empty

$var = "";

if (empty($var)) {
    echo "The variable 'var' is empty.";
} else {
    echo "The variable 'var' is not empty.";
}

Output:
“The variable ‘var’ is empty.

### Example 2: Checking a Non-Empty Variable

php
$var = “Hello”;

if (empty($var)) {
echo “The variable ‘var’ is empty.”;
} else {
echo “The variable ‘var’ is not empty.”;
}

**Output:**

The variable ‘var’ is not empty.

### Example 3: Checking an Array

php
$numbers = [];

if (empty($numbers)) {
echo “The array ‘numbers’ is empty.”;
} else {
echo “The array ‘numbers’ is not empty.”;
}

**Output:**

The array ‘numbers’ is empty.

Differences Between `isset()` and `empty()`
-------------------------------------------
1. `isset()` checks if a variable exists and is not `NULL`. It returns `false` if the variable is not set or if it is `NULL`.
2. `empty()` checks if a variable is considered "empty," which includes `0`, `"0"`, `""`, `NULL`, `false`, an empty array, and an unset variable. It returns `true` if the variable is empty.

Combined Example:
-----------------
You can use both `isset()` and `empty()` together to check if a variable is set and has a value:

php
$var = “”;

if (isset($var) && !empty($var)) {
echo “The variable ‘var’ is set and not empty.”;
} else {
echo “The variable ‘var’ is either not set or it is empty.”;
}

**Output:**

The variable ‘var’ is either not set or it is empty.
“`

Conclusion

• isset() is used to check if a variable is defined and is not NULL.
• empty() is used to check if a variable has a value that is considered “empty” in PHP.

These functions are essential for validating user input, ensuring variables are set before use, and avoiding errors in your PHP scripts.