It’s really weird that the C math library (math.h) doesn’t support the round function. It only includes the floor function which rounds down a float to an integer (can also be done by implicit or explicit casting) and the ceil function which rounds the value up.
x = floor(1.2);
x = floor(1.8);
x = (int)1.8;
x = 1.8;
x = ceil(1.2);
x = ceil(1.8);
The round function is supposed to round the float value to the nearest integer.
x = round(1.2);
x = round(1.8);
This can be done adding a
0.5 to the value and then truncating it.
x = (int)(1.2 + 0.5);
x = (int)(1.8 + 0.5);
We also have to take negative values into consideration by adding
-0.5 and then truncating.
x = (int)(-1.2 - 0.5);
x = (int)(-1.8 - 0.5);
Thus, here is the resulting C function:
int round(double number)
return (number >= 0) ? (int)(number + 0.5) : (int)(number - 0.5);
Note that you might want to use long rather than int to include support for larger numbers and avoid integer overflow.
That’s it, pretty much primitive, but fun!