Is my INT a FLOAT? Or Vice Versa

[s_mack]

newbie Q...

[s_mack]

related...

int = int / 10. Result is what? Int? Float? (presuming int not divisible by 10)

[PCM programmer]

If you want a floating point result, at least one of the variables in the
expression must be a floating point, or if it's a constant, the constant
must be written with a decimal point in the number. In a division
expression, at least one of the operations must be declared as a
floating point variable (or be written with a decimal point, if it's a constant).

Also, the variable that receives the result must be floating point.

If a function is to return a floating point value, it must specify that
in the function declaration.

An integer expression will result in an integer result. Any decimal
fraction will be truncated.

In other words, don't expect any 'magical' type promotions.

[s_mack]

No, I get you there. I do in fact want an INT result. But I want the right one

Riddle me this... does ccs for some reason roll over int8 values once they've reached their limit?

This should be a clear example (assume all items are int8):

250 + 50 = ?

I'd expect 255 (the highest int8 value). And from c++ specs I read that should be correct. Does CCS instead interpret that as 45? (rolled over at 255)

That would be consistent with the results I'm seeing. If that is the case, how do I correct? Declare _var as an int16 instead and then manually cap it?

[PCM programmer]

[s_mack]

thanks.

[FvM]

Generally, you should spend some time to learn more about the C-standard implicit type conversion and arithmetic processing rules. They are rather straightforward and allow to predict the result of the above questioned cases easily.

In the first example, a float conversion is performed during the calculation but followed by a conversion to int8. So the float factor should be considered correctly.

As already clarified by PCM programmer, modular overflow rather than saturation is the result of exceeding the number range in C arithmetic operations. The C standard committees are discussing fixed point extensions to the C language with saturation as required overflow handling, similar to respective libraries in the VHDL world.

[s_mack]

Thanks.

The point of confusion was a document I read (on wikipedia - by no means guaranteed reliable) which stated in no uncertain terms that when a data type's maximum (or minimum) value is exceeded that the variable takes on that maximum (or minimum) value.

I recognize that I lack a fundamental understanding.

I also lack a basic means of testing. Or, rather, I likely have such a means and am not aware of how to utilize it.

In PHP, I'd write some code open a browser and see what happens. With C++ I was handed a Microchip MPLAB ICD 2 device with pre-setup software on the computer and instructions on how to program our PIC devices. In other words, thrown into the pool (as shallow as it may be) without a lesson in the fundamentals of swimming. I don't know how to take these tools and even make a simple "hello world" work.

You are correct. I need to learn the basics. Whether that will happen or not I'm unsure. I'll continue to struggle along and seek help and see how far that gets me. If I find I run into something I can't do... well that's when the company has to get out its pocket book and either teach me to swim or hire a better lifeguard.

Cheers.

[FvM]

My point was to mention, that the C language has well-defined rules. It's not necessarily required to start C programming by learning them systematically. It's probably more instructive to learn them by the way, solving a problem. It's advisable however to have a language reference or a text book at hand.

Testing code on real hardware is pretty easy with a small PIC development board and an ICD or PICkit adapter. But also MPLAB SIM can give many insights, without any hardware.

[Ttelmah]

The problem is that without knowing the exact context of the Wiki quote, it may perfectly well be correct, but be being interpreted 'out of context', applying to a specific language or library.

The best 'reference' for C, is the original K&R 'C programming language', and possibly it's second edition, where ANSI starts to come along. This says for mathematical overflows:

"The handling of overflow, divide check, and other exceptions in expression evaluation, is not defined by the language. Most existing implementations of C ignore overflow in evaluation of signed integral expressions and assignments, but this behaviour is not guaranteed. Treatment of division by 0 and all floating point exceptions, varies among implementations; sometimes it is adjustable by a non-standard library function".

ANSI C, specifically defines unsigned integer overflows, to wrap (as CCS does).

At the end of the day, if you want a error-proof version, you just generate it. For instance:

[s_mack]

Thank you both. Most helpful.

[Ttelmah]

Except (of course) it should return temp, not _var.....

Best Wshs