Understanding the is_numeric() Function in PHP (With Examples)

When developing websites and applications with PHP, validating user input or data types is essential. One commonly used function for checking if a value is a number or numeric string is the is_numeric() function. In this article, we'll explore what is_numeric() does, how to use it with examples, and why it is important.

What is is_numeric() in PHP?

The is_numeric() function in PHP is used to determine whether a variable is a number or a numeric string.
It returns:

• TRUE if the value is a number or a numeric string
• FALSE otherwise

Syntax:

is_numeric(mixed $value): bool

Parameter:

• $value — The variable you want to check.

Return Type:

• Boolean (true or false)

Why Use is_numeric()?

In PHP development, ensuring that user input or function parameters are numeric can prevent errors and ensure your application runs smoothly. Common use cases include:

• Validating form inputs
• Performing mathematical operations
• Ensuring database integrity

PHP is_numeric() Function Examples

Example 1: Checking an Integer

$value = 123;
if (is_numeric($value)) {
    echo "$value is numeric.";
} else {
    echo "$value is not numeric.";
}
// Output: 123 is numeric.

Example 2: Checking a Numeric String

$value = "456";
if (is_numeric($value)) {
    echo "$value is numeric.";
} else {
    echo "$value is not numeric.";
}
// Output: 456 is numeric.

Example 3: Checking a Float

$value = 78.90;
if (is_numeric($value)) {
    echo "$value is numeric.";
} else {
    echo "$value is not numeric.";
}
// Output: 78.9 is numeric.

Example 4: Checking a Non-numeric String

$value = "Hello123";
if (is_numeric($value)) {
    echo "$value is numeric.";
} else {
    echo "$value is not numeric.";
}
// Output: Hello123 is not numeric.

Example 5: Checking Negative and Scientific Notation Numbers

$value1 = -123;
$value2 = "5e3"; // 5 x 10³ = 5000

echo is_numeric($value1) ? "$value1 is numeric.\n" : "$value1 is not numeric.\n";
echo is_numeric($value2) ? "$value2 is numeric.\n" : "$value2 is not numeric.\n";

// Output:
// -123 is numeric.
// 5e3 is numeric.

Important Notes about is_numeric()

• It accepts numbers in integer, float, scientific notation, and numeric strings.
• An empty string, null, or a non-numeric string will return false.
• Even strings like "0" or "0.0" are considered numeric.

Common Mistakes to Avoid

• Do not confuse is_numeric() with is_int() or is_float(). is_numeric() checks for both numbers and strings that look like numbers.
• If you need to check strictly for an integer or float (not a string), use is_int() or is_float() instead.