Question

Is there a function to round a float in C or do I need to write my own?

float conver = 45.592346543;

I would like to round the actual value to one decimal place, conver = 45.6.

Answer 1

As Rob mentioned, you probably just want to print the float to 1 decimal place. In this case, you can do something like the following:

#include <stdio.h> #include <stdlib.h>  int main() {   float conver = 45.592346543;   printf('conver is %0.1f\n',conver);   return 0; } 

If you want to actually round the stored value, that’s a little more complicated. For one, your one-decimal-place representation will rarely have an exact analog in floating-point. If you just want to get as close as possible, something like this might do the trick:

#include <stdio.h> #include <stdlib.h> #include <math.h>  int main() {   float conver = 45.592346543;   printf('conver is %0.1f\n',conver);    conver = conver*10.0f;   conver = (conver > (floor(conver)+0.5f)) ? ceil(conver) : floor(conver);   conver = conver/10.0f;    //If you're using C99 or better, rather than ANSI C/C89/C90, the following will also work.   //conver = roundf(conver*10.0f)/10.0f;    printf('conver is now %f\n',conver);   return 0; } 

I doubt this second example is what you’re looking for, but I included it for completeness. If you do require representing your numbers in this way internally, and not just on output, consider using a fixed-point representation instead.