Compare decimals in PHP

Question

I have a form input to get a number (it is a price). It can be a decimal like 102,5. I have to compare it with an other decimal for exemple 102,6. How can handle this ? I don't want to use round() cause i get to compare exactly.

score 8 · Answer 1 · edited May 23 '17 at 10:32

You could compare the absolute (i.e., numerical) difference to an "epsilon" (your "tolerance" ¹):

$epsilon = 0.01;
$diff = abs(102.5 - 102.6); // .1
if ($diff <= $epsilon) {
    // The numbers are equal
} else {
    // The numbers are not equal enough!
}

And, a little reading: "What Every Computer Scientist Should Know About Floating-Point Arithmetic" and "Comparing floating point numbers".

Also, you may find the follow SO questions (and answers!) interesting:

¹ That's right: You get to decide what makes the two numbers equal. It could be 0.1 (making 1.1 equal to 1.0), 0.01 (1.02 ~ 1.03) etc.

@Mamadou Are your numbers valid? What does `var_dump()` print? — jensgram, Sep 14 '10 at 11:07

score 4 · Answer 2 · answered Sep 14 '10 at 08:59

4

Don't store prices as floats, use integers (store cents, not dollars).

answered Sep 14 '10 at 08:59

user187291

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Good point. Didn't notice the "it is a price" part in the question :) – jensgram Sep 14 '10 at 09:04
Definitely makes more sense in terms of computing prices. – F.P Sep 14 '10 at 09:13

score 0 · Answer 3 · answered Sep 14 '10 at 09:09

0

Just make it decimal out of this format

$kinda_decimal = "102,5";
$kinda_decimal = floatval(str_replace(",",".",$kinda_decimal));

and compare it

answered Sep 14 '10 at 09:09

Your Common Sense

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okay ! the probleme is now when i choose the ( point ) it is not taken as a decimal coma ! I hope you understand ( am french)) – Mamadou Sep 14 '10 at 10:32

Compare decimals in PHP

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