What is the difference between "&&" and "||" and "and" and "or" in PHP? What to use?

Question

I have that question, what’s the difference between && and || and between and and or? Which one should I use?

Answer 1

The difference between them is in the order of precedence of each one.

Order of precedence? But what?!

For example, take the mathematical expression 3+4*2. What is the result of the expression? 14 or 11? The answer is 11, for the operator * has a higher precedence than the operator +.

In that case of &&, ||, and and or, the first two take greater precedence over the other two, otherwise they are identical.

In PHP there are also operators & and |, but these make comparisons bit-a-bit and between references, instead of the others cited, which make logical operations themselves.

Answer 2

This image illustrates the difference between the two logical operators.

Both operators result in a boolean value, i.e., true(true) or false(false).

And: $a and $b: Returns true if both past values are true.

Or: $a and $b: Returns true if $a or $b are true.

Xor: $a xor $b: Although you have not quoted this operator, it is similar to Or, returns true if $a or $b are true but not both.

!: ! $a: Unary operator, returns true if $a is not true.

&&: $a && $b: Binary operator, returns true if both $a how much $b are true.

||: $a || $b: Binary operator, returns true if $a or $b are true.

Precedence of Operators

As explained in Mutley’s response, the difference between these operators is in the precedence between them, or whatever the operator is evaluated first and which one will be evaluated next, as you can see in the following table, both && as || have priority over And and Or.

The following table shows the precedence of operators, from the highest precedence at the beginning to the lowest precedence.

Example

// AND
var_dump(  7 == 7  AND 9 > 7  );  // TRUE, ambas as expressões são verdadeiras
var_dump(  7 == 7  AND 9 < 7  );  // FALSE, apenas a primeira expressão é verdadeira

// OR
var_dump(  7 == 7  OR 9 > 7  );   // TRUE, ambas as expressões são verdadeiras
var_dump(  7 != 7  OR 9 > 7  );   // TRUE, a segunda expressão é verdadeira
var_dump(  7 != 7  OR 9 < 7  );   // FALSE, ambas as expressões são falsas

// XOR
var_dump(  7 == 7  XOR 9 > 7  );  // FALSE, ambas as expressões são verdadeiras
var_dump(  7 == 7  XOR 9 < 7  );  // TRUE, a primeira expressão é verdadeira
var_dump(  7 < 7  XOR 9 > 7  );   // TRUE, a segunda expressão é verdadeira

// !
var_dump(  ! 9 < 7  );   // TRUE, 9 NÃO é menor que 7
var_dump(  ! 9 > 7  );   // FALSE, 9 é maior que 7

// &&
var_dump(  7 == 7  && 9 > 7  );   // TRUE, ambas as expressões são verdadeiras
var_dump(  7 == 7  && 9 < 7  );   // FALSE, apenas a primeira expressão é verdadeira

// ||
var_dump(  7 == 7  || 9 > 7  );   // TRUE, ambas as expressões são verdadeiras
var_dump(  7 != 7  || 9 > 7  );   // TRUE, a segunda expressão é verdadeira
var_dump(  7 != 7  || 9 < 7  );   // FALSE, ambas as expressões são falsas

Demo

Reference: Comparison operators, logical operators and operator precedence in PHP

Answer 3

This is logical operators always result in a boolean value (true or false) and are often used where a conditional expression is expected.

&& results in true if his two operands are true, therefore it is common that these operands are relational.

|| reulta in true if at least one of the two operands is true.

and and or are equivalent to previous operators but has a precedence minor.

As the documentation shows in the first case the interpretation is this:

($e = (false || true))

In the second case it’s like this:

(($f = false) or true)

So in the first case the conditional expression using the operator || is more important and runs first. In the second case the second operand functions as something additional, the important thing is the previous assignment expression. This example does nothing useful, because it will always work $f = false and the true will never be executed.

Here comes a curiosity that not everyone knows. These operators work in short-circuit form, that is, if he can already anticipate the final result he does not continue running. In the case of the or if the first expression is already considered true, the second no longer needs to be executed, with a or just one of the two expressions is true. With the and the opposite occurs, if the first expression is false, the second does not need to be executed since it is impossible for the final result to be true, remembering that a and requires that both expressions must be true to result in true.

Answer 4

Operators && and || takes precedence over and and or. This determines the order in which they will be executed. && and || are executed before and and or.

Link to the Manual