math.h is a standard C header.
When you use it, on Linux (and other Unix varients) you must also use the "-lm" switch when linking, as in
This makes it include referenced functions from libm.a (or the equivilent).
gcc -o example example.c -lm
If your compiler package does not supply math.h and the math library, I'm surprised.
However, you can write your own round() function:
Note that this function may not have exactly the same results as using round(), but it should give you good values. I've not tested this code -- I just typed it in here -- but I think that it's correct. I've not commented it, so see if you can figure out what it does and how it does it.
double myround(double value, int places)
double adjust = 1.0;
for (;places > 0; places--)
adjust *= 10;
temp = (long)((value * adjust) + 0.5);
return (double)temp / adjust;