floating points and maths

[brian m]

Quick question for you all.


i'm trying to do some calculations, i'm decalring some variables as doubles, however i'm getting an error saying it can't handle floating points.

does anybody know how to overcome this i need to be able to display decimals on my lcd for a project i'm doing.

also i can multiply no problem but divison doesn't work. any suggestions.

i'm using a 16f877 and not to sure of the ccs version.

[PCM programmer]

The double data type is not supported. You have to
declare them as float. Example:

float my_value;

To find your compiler version, compile a source file
without errors and then look at the top of the .LST file.
Example:

Compile TEST.C

Then look at TEST.LST

[Guest]

float doesn't seem tobe working.

its only accepting ints, whcih are only 8 bit so its giving a range of -127 to +127

any ideas.

[SherpaDoug]

Just because you need to display decimals in your output doesn't mean you have to use floats. Floating point numbers use a lot of processor resources and should be avoided if at all possible.

Instead consider using scaled integers. If you need to display temperature to 1/100 of a degree, consider calculating it in integer "centidegrees." A signed long can then hold +/-327.68 degrees, enough for many applications.

As many on this list know I previously worked on a product that measured ship hulls, looking for rust, dents, warpage, etc.. We did our measurements in 24 bit integer millimeters. We could cover anything from the depth of a dent to the length of a supertanker. We did need another number format for measuring steel and paint thickness, 16 bit integer mils.

When we displayed data we would either print it to a string and use string functions to insert decimal points and commas in appropriate places, or use / and % to break the number where needed for printing. It took a little more programming effort than just declairing everything as huge floats, but the processing power required was dramatically lower and round-off errors were exactly predictable.
_________________
The search for better is endless. Instead simply find very good and get the job done.

[Ttelmah]

[Thomas Blake]

While I agree that something is goofy, perhaps even your compiler, I also agree that you should avoid floating point and use fixed-point as mentioned above. Essentially you should do a high-precision result, convert to BCD (assuming that's what your display accepts) and then just turn on the decimal point at the proper position on your display. You really should move the decimal point position for scale change if that is visually acceptable, because it's much simpler than any other way.

Another advantage of doing that is that you don't have to worry about IEEE-to-display format conversion. BCD is irritating enough as it is!

tcb

[brian m]

i've manged to sole the problem.

int count=0;
float speed=0;



speed=((float)count*(float)(22.00/7.00)*2*33);
printf(lcd_putc,"\n");


printf(lcd_putc,"\nC= %d,secs= %3.2f",count,speed);