Say I have a string, $char. $char == "*".
I also have two variables, $a and $b, which equal "4" and "5" respectively.
How do I get the result of $a $char $b, ie 4 * 5 ?
Thanks :)
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7 Answers
You can use eval() as suggested by @konforce, however the safest route would be something like:
$left = (int)$a;
$right = (int)$b;
$result = 0;
switch($char){
case "*":
$result = $left * $right;
break;
case "+";
$result = $left + $right;
break;
// etc
}
1 Comment
Fela Maslen
that's the answer I was looking for :)
safest method is a switch construct:
function my_operator($a, $b, $char) {
switch($char) {
case '=': return $a = $b;
case '*': return $a * $b;
case '+': return $a + $b;
etc...
}
}
4 Comments
Fela Maslen
yep...people answer too fast!
Shakti Singh
if the operator is
= your code will produce sum of operands. Should not there be a break?
Marc B
The '=' wouldn't do anything in this case, unless $a was passed in as a reference. The assignment would be lost as soon as the function returns, otherwise. It's just an example.
Svish
@ShaktiSingh No need for
break when there's returnThe easiest but most dangerous method is to use eval.
$c = eval("return $a $char $b;");
5 Comments
Fela Maslen
I'd rather not use eval as the values come from user input.
Shakti Singh
@konforce: At last all we have to use the code in production they why we suggest eval
Matthew
@Fela, you should always be validating the user input whether you use
eval or not. If you are validating that $a and $b are proper numbers and that $char is a proper operation then eval will be safe. That said, I would still not use eval on a public site.
fingerman
if it's a local project, there is no reason not to use
eval.Fela Maslen
I'm not using eval, I'm using switches with different operators. All user input is sanitised of course.
Another way to avoid creating a switch/case, could be:
<?php
// Doesn't matter if $a and $b are integers or strings
$a = 100;
$b = 1000;
$operator = ">";
$operations = [
'=' => $a == $b,
'>' => $a > $b,
'>=' => $a >= $b,
'<' => $a < $b,
'<=' => $a <= $b,
'<>' => $a <> $b,
];
// It will get the value of $a > $b and the result will be false
$operations[$operator]
?>
Finally if you prefer, you can move the $operations array, to a function to improve the readability code.
<?php
// Doesn't matter if $a and $b are integers or strings
$a = 100;
$b = 1000;
$operator = ">";
// It will get the value of $a > $b and the result will be false
$result = getOperationResult($a, $b, $operator);
function getOperationResult(string|int $a, string|int $b, string $operator): bool
{
$operations = [
'=' => $a == $b,
'>' => $a > $b,
'>=' => $a >= $b,
'<' => $a < $b,
'<=' => $a <= $b,
'<>' => $a <> $b,
];
return $operations[$operator];
}
?>
Comments
take a look at the eval() function. you will need to build a proper php command and run inside the eval() to extract out the result.
Comments
You can do with eval however I would not suggest using eval.
If there is case operator can by anything you should check what operator is before using
switch($char)
{
case '*':
$result= $a * $b;
break;
case '+':
$result= $a + $b;
break;
}
1 Comment
Fela Maslen
Yes, I'm going to go with that option. Thanks :)
<?php
$a = 'alex';
$b = "alex";
$c = "==";
function abc($a,$b,$c){
$d = 'return ($a '.$c.' $b) ? true : false;';
return eval($d);
}
if(abc($a,$b,$c)){
echo "condition true";
}else{
echo "condition false";
}
// echo $e;
?>
1 Comment
toing_toing
please explain your solution