intdiv() performs true integer division and is safer for whole numbers, while casting (int) after division risks floating-point precision errors. 2. Both truncate toward zero, but casting can yield incorrect results with negative or imprecise values due to float representation issues. 3. intdiv() throws a DivisionByZeroError on zero divisor, whereas (int)(5/0) results in 0 after converting INF, with only a warning. 4. Use intdiv() for clear, reliable integer division with integers; use casting only when handling mixed or float inputs, but validate carefully to avoid precision loss. When performing integer division in PHP, prefer intdiv() for correctness and clarity.

When working with integers in PHP, division might not behave exactly as you expect—especially when you need clean, whole-number results. Two common approaches pop up: using the intdiv() function and casting the result of regular division to an integer. While both can give you integer results, they work differently under the hood and can produce different outcomes depending on the input. Let's break down the key differences and when to use each.

What Is intdiv()?

intdiv() is a built-in PHP function introduced in PHP 7 that performs integer division—meaning it divides two integers and returns the quotient as an integer, truncating any remainder toward zero.

Syntax:

intdiv(int $dividend, int $divisor): int

Example:

echo intdiv(7, 2);  // Output: 3
echo intdiv(-7, 2); // Output: -3

This function is specifically designed for integer arithmetic and will throw a DivisionByZeroError if the divisor is zero.

What Happens When You Cast Division Results?

An alternative approach is to use regular division (/) and then cast the result to an integer using (int):

echo (int)(7 / 2);  // Output: 3
echo (int)(-7 / 2); // Output: -3

At first glance, this looks identical to intdiv(). But the devil is in the details—especially when dealing with negative numbers or floating-point precision issues.

Key Differences: intdiv() vs. Casting

1. Behavior with Negative Numbers

Both methods truncate toward zero (they don’t floor), so they behave similarly in most cases:

intdiv(-9, 4);     // -2
(int)(-9 / 4);     // -2

? So far, so good. But things get risky when floating-point inaccuracies come into play.

2. Floating-Point Precision Pitfalls

Regular division (/) returns a float, and floats can have tiny precision errors:

$x = (int)(7 / 0.1); // 7 / 0.1 = 70, right?
var_dump($x);       // int(69) ???!

Wait—what? Because 0.1 can't be represented exactly in binary floating-point, 7 / 0.1 might evaluate to something like 69.999999, and casting to (int) truncates the decimal, giving 69.

But intdiv() only accepts integers, so this exact scenario wouldn't occur—because you'd be working with whole numbers from the start.

3. Type Safety and Input Validation

intdiv() requires integer operands. If you pass floats, PHP will cast them to integers silently, which can lead to unexpected behavior:

intdiv(7.9, 2.1); // Actually computes intdiv(7, 2) → 3

So even though intdiv() is type-declared for integers, PHP coerces floats to ints without warning.

Meanwhile, casting after division doesn’t care about input types—it just divides whatever you give it and truncates the float result.

When Should You Use Each?

Here’s a quick guide:

• ? Use intdiv() when:

  • You're certain you're working with integers.
  • You want semantically clear, intentional integer division.
  • You prefer built-in functions over manual casting for readability.
  • You want explicit error handling for division by zero (exception vs silent INF or false).

• ? Use casting ((int)($a / $b)) when:

  • Inputs might be floats or mixed types.
  • You're doing non-integer-based scaling or unit conversions.
  • But be cautious: always validate or round if precision matters.

?? Avoid casting when high precision is critical—consider round() or floor() instead, depending on your rounding needs.

Bonus: Edge Cases and Division by Zero

For example:

$n = PHP_INT_MAX;
var_dump((int)($n / 1)); // Might not equal PHP_INT_MAX due to float precision loss!

Summary

• intdiv() is safer and clearer for true integer division.
• Casting after / is more flexible but fragile due to floating-point quirks.
• Both truncate toward zero, but casting risks precision loss.
• Always validate inputs and consider edge cases like zero divisors and large numbers.

If you're doing math that should stay in the integer domain, prefer intdiv()—it’s more predictable, explicit, and less prone to silent bugs.

Basically: when you mean integer division, use intdiv(). Don’t rely on casting unless you really need float inputs—and even then, tread carefully.

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