Float division with two int16

[global]

Hello, i'am actually programming a PIC 16F877A with CCS 3.150, i'am trying to do a division between two int16 variables and put the result in a float variable.

This is my code:

*****

int16 Current=0;
int16 Capacity=0;
float Time=0;
.......
Current=Readcurrent();
Capacity=(int8)Readcapacity();
Current=abs(Current);
Time=Capacity/current;
printf("remaining time %f" , Time);
printf(lcd_putc,"\fremaining time \n %f" ,Time);
*****

if Capcity=3, and Current=2, the result will be 1,99999
if Capcity=12, and Current=4, the result will be 3.99999
the result on the LCD and on the Serial is the same.


I don't know why the result is not good.
Thanks for your help.
Bruno

[mvaraujo]

Bruno,

I don't have the compiler here to test up, but try to:

[Humberto]

CCS has some non ANSI rules with casts, automatic casting not always
happen as expected.

Try this:

Time= (float)Capacity / (float)current;

Humberto

[SherpaDoug]

This looks bad:

int16 Current=0;
int16 Capacity=0;
float Time=0;

Time=Capacity/current;

According the proper C convention the PIC will divide the integer Capacity by the integer current producing an integer result. Then it will cast this integer result to a float and assign it to Time.

You probably want:

Time=(float)Capacity/(float)current;

This will cast Capacity and current to floats so that the compiler will do a floating point division.
_________________
The search for better is endless. Instead simply find very good and get the job done.

[SherpaDoug]

[mvaraujo]

Hi SherpaDoug,

Really? I don't work very often with floats on PIC.

So what do you suggest?

Best regards,

Marcus

[Guest]

Kernighan & Ritchie is the ANSI C bible

[mvaraujo]

I don't know if you "guest" intended to expose my ignorance on C but I can say that your damn right!

I started working on uc assembly, went to C compilers to make some things easier but I'm that kind of guy that always read the list file to see if on assembly it seems reasonable. In summary, as programmer, if feel much like an engineer!

As some others, I would like to see the right answer to the guy, so we can all learn.

Regards,

Marcus

[DragonPIC]

Sorry I didn't sign in. I just wanted you to know, so you are informed. People look to this book because it was written by the designer.
_________________
-Matt

[mvaraujo]

Hi Matt,

Thanks for the reference!

I was just kidding with my last message. We're all learning, right? At least in different levels!

Take care!

Marcus

[DragonPIC]

yeah, I didn't know what a cast was a year ago.
_________________
-Matt

[SherpaDoug]

[global]

Thanks for your help, it's now working well using :

Time= (float)Capacity / (float)current;

best regards,
Bruno