"+=" operator, comments appreciated...

  • Thread starter Thread starter almurph
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A

almurph

Hi,

Just wondwering is a difference between the "+=" operator between C
and C#?


I ask as I have reverse engineered some C code to C# and am receiving
some differing results. I have traced it down to a line involving a
"+=" operator. The C clode uses floats but I am using double, but this
should not make a difference right?

Just wondering if anyone has any comments or suggestions or user
experiences that thay would like to share.

Thank,
Al.
 
Just wondwering is a difference between the "+=" operator between C
and C#?


I ask as I have reverse engineered some C code to C# and am receiving
some differing results. I have traced it down to a line involving a
"+=" operator. The C clode uses floats but I am using double, but this
should not make a difference right?
Click to expand...
Let's see. "float" is not the same as "double", so how on earth would you
reach the conclusion that using different types could make no difference?

Without seeing your code it's impossible to say anything conclusive. That
said, "float" and "double" are both floating-point types (in both C and C#),
but "double" has more precision (in C#; in C it *usually* has more
precision, but this is platform-dependent). Floating-point addition with
different precision *is* going to give different results.
 
Just wondering if anyone has any comments or suggestions or user
experiences that thay would like to share.
Click to expand...

My experience suggests that questions like "I get differing code when I use
+=, can anyone tell me why" generally get ripped apart for not providing any
useful information from which to even understand the question let alone
produce an answer :-)
 
Peter Morris said:
My experience suggests that questions like "I get differing code when I use
+=, can anyone tell me why" generally get ripped apart for not providing any
useful information from which to even understand the question let alone
produce an answer :-)
Click to expand...

And since the variable being used in this += line is a floating point
variable, the very first thing that should be suspected is that the
floating point value(s) aren't what you think they are.
 
[email protected] said:
I ask as I have reverse engineered some C code to C# and am receiving
some differing results. I have traced it down to a line involving a
"+=" operator. The C clode uses floats but I am using double, but this
should not make a difference right?
Click to expand...

x = 0.000000001;
y = 4.0;
y += x;

That will definitely produce different results with singles and doubles.
 
Hi,

Just wondwering is a difference between the "+=" operator between C
and C#?


I ask as I have reverse engineered some C code to C# and am receiving
some differing results. I have traced it down to a line involving a
"+=" operator. The C clode uses floats but I am using double, but this
should not make a difference right?

Just wondering if anyone has any comments or suggestions or user
experiences that thay would like to share.

Thank,
Al.
Click to expand...

In C++ the += operator has it's own meaning and can be overloaded, in C#
it's just defined to use the + operator.

In C# this code:

d += 1.0;

is exactly the same as:

d = d + 1.0;

As the += is a bit more predictable in C# than C++, it's not likely that
it is the += operation in itself that is the problem. Perhaps you have
some other expression that is handled differently. What else is there on
the line?
 
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