How can I round up when performing division on two int values in C++ without using std::ceil?
Typically I end up doing something like the following:
double res = ceil(a / (double) b);
Is there any way I can duplicate the result without using std::ceil?
If a and b are both positive, you can avoid floating point completely and get both exact results (no problems with FP rounding) and faster execution time through the classical method:
int res = (a + (b - 1)) / b;
For negative a you don't need any correction - the truncation performed by integer division already has the semantics matching your ceil formula; so, if you want a more general case:
int res = (a<0 ? a : (a + (b - 1))) / b;
you could do this
double res = (double) (((a % b) == 0) ? (a / b) : (a / b) + 1);
basically if there is a remainder, add 1 to the truncated integer result