&& and is the same logical function in PHP, but the priority is different, resulting in different execution orders; && priority is higher than and and and is lower than the assignment operator =; therefore $success = true and false is actually parsed to ($success = true) and false, making $success still true; 1. Use && and || in conditional judgments; 2. Use and and or only in control flows (such as $file = fopen() or die()); 3. Complex expressions should use brackets to clarify priority; 4. Avoid mixing and/or in assignments unless explicitly intended; in short, although the two are logically equivalent, usage scenarios must be distinguished due to differences in priority to prevent logical errors.

When writing PHP code, you might have seen both && and and used for logical operations — sometimes interchangeably, sometimes not. At first glance, they seem to do the same thing: evaluate whether two conditions are true. But there's a subtle yet critical difference between && and and in PHP that can lead to unexpected bugs if misunderstood. Let's break it down.

They're Not Equal — Operator Precedence Matters

The key difference between && and and lies in operator precedence — that is, the order in which operators are evaluated in an expression.

• && has a higher precedence than and .
• In fact, and has very low precedence , lower than assignment ( = ), which can drastically change how your code behaves.

Let's see this in action:

 $success = true && false;
var_dump($success); // bool(false)

This works as expected. But now try using and :

 $success = true and false;
var_dump($success); // bool(true) — Wait, what?!

Why is it true ?

Because of how PHP parses the expression due to precedence:

 // This is actually interpreted as:
($success = true) and false;

So $success gets assigned true , and then the and false part is evaluated but doesn't affect the variable. The full expression evaluates to false , but the assignment already happened.

This is a common trap .

Practical Example: Chaining Operations

This issue often surfaces when combining assignment and logic:

 $result = getData() or die('No data');

This pattern is actually safe because or (like and ) has low precedence. It's interpreted as:

 ($result = getData()) or die('No data');

So if getData() returns false , the assignment still happens, and then die() is triggered.

But if you used || instead:

 $result = getData() || die('No data');

That would be parsed as:

 $result = (getData() || die('No data'));

Which means die() only runs if getData() is false, but the result of the entire expression (true/false) is assigned to $result , not the actual data. So you lose your data!

So When Should You Use Which?

Here's a practical guide:

• ? Use && and || for logical conditions inside if , while , etc.

   if ($userValid && $inputValid) { ... }

• ? Use and and or only when you want low precedence for control flow (eg, error handling).

   $file = fopen('data.txt', 'r') or die('Cannot open file');

• ? Avoid mixing and / or with assignment unless you explicitly understand and intend the behavior.

Quick Reference: Precedence Levels (High to Low)

So in expressions involving multiple operators, && binds tighter than and , and both and and or are weaker than assignment.

Best Practices

To avoid confusion:

• Stick with && and || in most conditional logic.
• Use parentsthes when in doubt:

   if (($active == true) and ($admin == true)) { ... }

• Avoid relying on and / or unless you're using them for control flow patterns (like the die() example).
• Be extra cautious in complex expressions.

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Basically, && and and do the same logical operation — but when they happen in an expression is completely different. That tiny difference in precedence can lead to major logic bugs.

So while they may look interchangeable, treat them as distinct tools for different jobs.

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