Have tried for a while to figure out.
have a simpel number, ex 1, when add 1 it show 2.
when subtract 1 it show 1 Again, and next 0 , but then it show 32767 instead of -1 why ??
number is declared as signed integer.

offsetgrad--;    
  lcd_goto(0x0e);
  utoa(offgrad, offsetgrad, 10);
  lcd_puts(offgrad);

 

what is the data type of offsetgrad?

 

signed int offsetgrad;

 

utoa function is used for converting unsigned numbers to ASCII. For signed numbers try the itoa function Every signed argument passed to the utoa function will come out the other end as a unsigned argument. In the binary system the integer number -1 is 0xFFFF

 

The reason is signed integer numbers are represented as a two's compliment number. <= Do stop and read that link.

So when you subtract 1 from zero you get -1, which as a 2's compliment integer is represented by 111 1111 1111 1111.

When you pass that to utoa() the number is taken as an unsigned integer, so it looks like a big positive number.

 

utoa function is used for converting unsigned numbers to ASCII. For signed numbers try the itoa function Every signed argument passed to the utoa function will come out the other end as a unsigned argument. In the binary system the integer number -1 is 0xFFFF

Takker.
that Works.
need to make changes in the temperature Circuit, the voltage drops to much when wire is around 10 m. to the sensor.