Signal Conversion in C
You just need to use a typecast:

/* ... */
float fres;
unsigned char ires_mohm;

fres = get_resistance();
ires_mohm = (unsigned char)((1000 * fres)+0.5);
/* ... */


The added "0.5" is because float to integer conversion is done by truncation rather than rounding.

You would also want to do some error checking in case the floating point value is less than 0 or greater than 0.2554.