Using 'and' and 'or' in an if/else PHP statement

Question

I am attempting to use both AND and OR statements in my IF/ELSE statement, but I cannot get the desired effect.

What I would like to achieve is that if either 'a' or 'b' has a value of '1' but both 'c' and 'd' must be 1 then I get 'Yes'.

All my attempts have given me either 'Yes' or have not worked (blank screen).

<?php
$a = "0";
$b = "1";
$c = "1";
$d = "1";
if (($a == "1") || ($b == "1") && ($c == "1") && ($d == "1")) {
    echo "Yes";
    }
    else {
    echo "No";
    }

?>

Thank you.

Incidentally, the parentheses around the equality expressions aren't really needed. — Don't Panic, Nov 07 '16 at 18:35

Felippe Duarte · Accepted Answer · 2016-11-07T18:27:00.773

3

You need and extra parenthesis, to make sure the evaluation order will be done correctly, like in math:

if (  (  ($a == "1") || ($b == "1")  ) && ($c == "1") && ($d == "1")) {
      ^                              ^

That way, let's say for example:

$a = 1;
$b = 2;
$c = 1;
$d = 2;

The first parenthesis will be evaluated as true || false. The final result will be true.

So now you have true && ($c == "1") && ($d == "1")

$c = 1, so again, the next evaluation will be true && true && ($d == 1)

$d = 2, so the next round will be true && true && false, final result, in this example, will be false.

edited Nov 07 '16 at 18:27

answered Nov 07 '16 at 18:23

Felippe Duarte

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That's the chap! Thank you @Felippe Will accept answer when allowed (in 11 minutes!) – omega1 Nov 07 '16 at 18:26

Paul Carlton · Answer 2 · 2016-11-07T18:39:15.887

You need to add parenthesis.

Why?

Because inner parenthesis are evaluated first before outer parenthesis. Take this example:

((1 == 1 && (2 == 2)) || 3 == 3)

What will be evaluated first? The 2 == 2 then the 1 == 1 and then the 3 == 3. In your if condition, because you are mixing AND's and OR's, you will not get the desired affect.

( (($a == "1") || ($b == "1")) && ($c == "1") && ($d == "1") )

Should work for you. In fact you can do this so that it looks even better:

(($a == 1 || $b == 1) && $c == 1 && $d == 1)

Because it is not necessary to put 1 in quotes ie: "1". PHP's truthiness will evaluate 1 == "1" to be true. However if you wanted to check for an actual string that contains 1, then you would use the === operator.

$a = 1;
$b = "1"
$a == "1";  // true
$b == 1;    // true
$a === "1"; // false
$b === "1"; // true

However for more information go here: http://php.net/manual/en/language.operators.precedence.php

score 0 · Answer 3 · edited May 23 '17 at 12:01

0

The equality operators will be evaluated first, then &&, then ||. Parentheses will be evaluated before anything else, so adding them can change the order.

Check the answer In Java, what are the boolean "order of operations"?

edited May 23 '17 at 12:01

Community

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answered Nov 07 '16 at 18:27

Nandan Bhat

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score 0 · Answer 4 · answered Nov 07 '16 at 18:29

It will always echo a Yes because PHP interpreter places The AND operation before the OR operation.

So your if statement interpretes like this:

If a = 1 or b = 1 and c = 1 and d = 1 then echo 'Yes' else echo 'No'

That's why you always get a yes..

Using 'and' and 'or' in an if/else PHP statement

4 Answers4