I have an array of float data type of which I tried to change them to round numbers by casting them to unsigned char data type. But for data such as 3.99, the result of the casting is 3. What can I do so that all the data will be rounded to their nearest values?

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you can round it to any place you want, including the ones, with the following method:

#include <math.h>

void RoundOff ( float & TheNumber, int ThePlace)
// the place is the power of ten you are rounding it to, for
// example an input of -2 will round it to the hundreths place
// an input of 0 will yield the number rounded to the ones place

   float PlaceMultiple = pow ( 10, ThePlace ) ;

   TheNumber = ( ( int ) (TheNumber / PlaceMultiple + 0.5 ) )  
                          *  PlaceMultiple;

thats all there is to it.  it will round to the nearest of any place you specify and you dont even have to cast it as a char to do it!
For unsigned chars, (char)(3.99+0.5) would give the nearest value.
(If you don't insist on round-to-even for 4.5)
I thought the idea was to have an unsigned char?

If you're not unsigned, RoundOff will fail when TheNumber is negative.
It will also fail when TheNumber is not in the range of (int)
if you really need to do it for negatives just add the following inside the method:

int Sign = 0;

if(TheNumber < 0) Sign = -1;
else Sign = 1;

and then multiply it by the 0.5 like:

TheNumber = ( ( int ) ( TheNumber / PlaceMultiple +
                         ( Sign * 0.5 ) ) ) * PlaceMultiple;

if an int doesnt give you enough room replace the ( int ) with a ( long ).  if even thats not enough you can resort to bit crunching but since you were going to cast it as a char that should be more than enough.

anything else?
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