Floating point operation returns different result in PHP and C#

Question

I get different results when try to division same numbers in PHP and C#:

PHP:

echo 1000/0.03475; 
output:28776.9784173

C#:

1000/0.03475
output:28776,9784172662

Why? And how to get same results?

Answer 1

Because that's how they're being displayed.

printf("%.10f\n", 1000 / 0.03475);

Answer 2

But they do give the very same result, just rounded to different numbers of decimal places when displayed. If you were to look at the actual bits representing the floating-point number in memory, they ought to be identical (given the same architecture).

Answer 3

What the other answers say is probably the reason you have different values (more accurately, different rounding in display).

However, in PHP a float as the same semantincs a C double (it usually has 64 bits) has (additionally, PHP targets C89, while only C99 defined floating point arithmetic so that it complies with IEEE 754):

The C89 standard does not even require IEEE format, and for C99, full IEEE 754 support (Inf, NaN, denormals) is optional.

In C# a float is 32-bit wide and is guaranteed to be (mostly) IEEE 754 compliant. The closest thing to PHP's float would be C# double.

Answer 4

There are two possibilities, as others have said: either they're the same floating-point value, but just printing differently, or they're different floating-point values. To see if they're the same, you need to print all the decimal digits -- if your language allows (C# and PHP don't -- see my article http://www.exploringbinary.com/print-precision-of-dyadic-fractions-varies-by-language/).

They could be different floating-point values because not all compilers/interpreters/run-time libraries convert every decimal string to the correct floating-point number (in your example, I'm talking about the 0.03475 part in particular). See my article http://www.exploringbinary.com/incorrectly-rounded-conversions-in-visual-c-plus-plus/ for more details.