How to count with an array of operators

Question

$operators = array(
    "+",
    "-",
    "*",
    "/"
);

foreach($operators as $key => $opp){
    //echo "key: $key, opperator: $opp <br />";
    echo $result = 4 . $opp . 4 . "<br />";
}

why isn't my code counting the possible combinations?

like:

echo $result = 4 + 4;

8

I think it's because +, -, *, / is here as string, not as operator. — Lkopo, Oct 19 '13 at 19:00
[How to make a calculator in PHP](http://stackoverflow.com/questions/12692727/how-to-make-a-calculator-in-php) — Mark Baker, Oct 19 '13 at 19:12
Two answers using eval() and neither of them highlight the dangers or problems of it. — Mark Baker, Oct 19 '13 at 19:14

score 2 · Answer 1 · answered Oct 19 '13 at 19:06

2

Dot (".") is concatenation operator for strings in PHP. Dynamic typization makes all this a string. Actually you get same as:

echo $result = "4 + 4 <br />";

Use eval as said in prev answer.

foreach($operators as $key => $opp){
    echo $result = eval("echo 4 $opp 4;") . "<br />"; // eval should contain valid code
}

answered Oct 19 '13 at 19:06

: Parse error: syntax error, unexpected end of file in D: eval()'d code on line 1 – vdhmartijn Oct 19 '13 at 19:10
Sorry) Already edited with valid code. eval can perform only valid one, which simple "4 + 4" isn't. – Oct 19 '13 at 19:13
Thank you verry much for your help! – vdhmartijn Oct 19 '13 at 19:13

score 2 · Accepted Answer · answered Oct 19 '13 at 19:17

2

You can avoid eval using some anon functions, 5.3+ required

$operators = array(
    "+" => function($l,$r) { return $l + $r; },
    "-" => function($l,$r) { return $l - $r; },
    "*" => function($l,$r) { return $l * $r; },
    "/" => function($l,$r) { return $l / $r; },
);

foreach($operators as $key => $opp){
    //echo "key: $key, opperator: $opp <br />";
    echo $result = $opp(4,4). "<br />";
}

answered Oct 19 '13 at 19:17

Matthew Scragg

4,540
3
19
27

This answer brings me the most! – vdhmartijn Oct 19 '13 at 19:59

Jelle Ferwerda · Answer 3 · 2013-10-19T19:48:32.320

1

Because you are just doing something with strings. They're not treated as operators.

You could of course use eval:

$x = eval(4 . $opp . 4 );
echo $x;

edited Oct 19 '13 at 19:48

answered Oct 19 '13 at 19:02

Jelle Ferwerda

1,254
1
7
13

How to count with an array of operators

3 Answers3