Wrong calculations in PHP - php

Question

I am trying to calculate in PHP. When I try to do that I can see that the result is mostly wrong.
The script I am using is the following:
$newrate = 1 / $rate["rate"];
echo '1 /'. $rate["rate"]. ' = '.$newrate;
The result I get is the following:
1 /1.0867 = 1
1 /117.01 = 0.0085470085470085
1 /1.9558 = 1
1 /27.534 = 0.037037037037037
1 /7.4589 = 0.14285714285714
1 /1.0867 should be 0.92021717125 and not 1.
I can reproduce this step by adding the following line to my script:
$rate["rate"] = 1.0867;
When I run the script the result is still 1. When I change my script like:
$newrate = 1 / 1.0867;
echo '1 / 1.0867 = '.$newrate;
I get a correct result. The output is then: 0.92021717125.
Does someone know what is wrong with this script? What is the reason that my script is making incorrect calculations?
Update 1:
Here is my full script:
<?php
$XML=simplexml_load_file("https://www.ecb.europa.eu/stats/eurofxref/eurofxref-hist-90d.xml");
foreach($XML->Cube->Cube as $rat)
{
foreach($rat as $rate)
{
$newrate = '1' / $rate["rate"];
echo '1 /' . $rate["rate"] . ' = ' . $newrate;
echo '<br /><br />';
}
}
?>

Answer 1

I think there is something wrong with your example. I tested exactly what you described and works as expected.
<?php
$rate = [];
$rate["rate"] = "1.0867";
$newrate = 1 / $rate["rate"];
echo '1 / ' . $rate["rate"] . ' = ' . $newrate;
// 1 / 1.0867 = 0.92021717125242
You can see it running here
https://repl.it/#thiagodamata/NeighboringPeachpuffArchitect
Probably, you are using "," instead of "." when sending the number.
PHP cast the number only until it hits something unexpected. So "1,0867" is cast to 1. It is a classic problem when dealing with numbers in different formats, considering different languages.
<?php
// simulating the "," error
$rate["rate"] = "1,0867";
$newrate = 1 / $rate["rate"];
echo '1 / ' . $rate["rate"] . ' = ' . $newrate;
// 1 / 1,0867 = 1
Take a look in this thread about how to cast the number from different languages masks PHP: Locale aware number format and take a deeper look into the PHP function number-format https://www.php.net/manual/en/function.number_format.php
Update - After getting the full code example
Looking to your full code becomes more clear the problem. The var that you are getting in the loop it is a SimpleXmlElement, not a string. So, SimpleXmlElement is printed as the "1.0867" but it is not its real value.
To make the SimpleXmlElement cast to float properly, you need to use the cast function.
<?php
$XML=simplexml_load_file("https://www.ecb.europa.eu/stats/eurofxref/eurofxref-hist-90d.xml");
foreach($XML->Cube->Cube as $rat)
{
foreach($rat as $rate)
{
print(var_dump($rate["rate"]));
/*
object(SimpleXMLElement)#7 (1) {
[0]=>
string(6) "1.0867"
}
*/
print("class = [" . get_class($rate["rate"]) . "]\n");
// class = [SimpleXMLElement]
print("as string = [" . $rate["rate"] . "]\n");
// as string = [1.0867]
print("without cast = [" . (1 * $rate["rate"]) . "]\n");
// without cast = [1]
$a = (float)($rate["rate"]);
print("with cast = [" . ($a) . "]\n");
// with cast = [1.0867]
print(serialize($a));
//d:1.0867;
$newrate = '1' / $a;
echo '1 / ' . $a . ' = ' . $newrate . "\n";
// 1 / 1.0867 = 0.92021717125242
echo '<br /><br />';
exit();
}
}
?>
You can see this running here:
https://repl.it/#thiagodamata/FuchsiaLightheartedPrintablecharacter
Just printing the value of a var does not always give you the real value of some object. There are other functions like var_export https://www.php.net/manual/en/function.var-export.php, var_dump https://www.php.net/manual/en/function.var-dump.php and serialize that may help you to see the real value of the vars.

Answer 2

Calculations are fine, and correct
You've not taken into account implicit type casting in PHP. Try this:
<?php
print "integer divided by float = " . (1 /1.0867) . "\n"; // returns 0.9202171712524
print "Integer divided by string = " . ((1/"1.0867") . "\n"; // returns 1
You are expecting PHP to know what your intention is when you throw a tring into an arithmetic operation - that's not how PHP works.
Just because it is dynamically typed doesn't mean you don't need to be careful with your data types.
print (1/(float)$rate['rate'];

Answer 3

try cast all values as a float
echo 1.0 / (float) $rate['rate'];