C Round Function
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.
For example,
int x; x = floor(1.2); // x is set to 1 x = floor(1.8); // x is set to 1 x = (int)1.8; // x is set to 1 (Explicit Narrowing Conversion) x = 1.8; // x is set to 1 (Implicit Narrowing Conversion) x = ceil(1.2); // x is set to 2 x = ceil(1.8); // x is set to 2
The round function is supposed to round the float value to the nearest integer.
x = round(1.2); // x is set to 1 x = round(1.8); // x is set to 2
This can be done adding a 0.5 to the value and then truncating it.
x = (int)(1.2 + 0.5); // x is set to 1 x = (int)(1.8 + 0.5); // x is set to 2
We also have to take negative values into consideration by adding -0.5 and then truncating.
x = (int)(-1.2 - 0.5); // x is set to -1 x = (int)(-1.8 - 0.5); // x is set to -2
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!
Enjoy!
Ali B
Two other options; just use floor(x+.5) or make a macro- #define round(X) floor((X)+.5)
You are right. floor(x+.5) is just the same as (int)(x+.5). But you forgot to take negative values into consideration.
Interestingly, I even nedumala about it …
Very useful – thanks. Also, I like davidhilton’s idea of turning your function into a macro.
I like to see the code applied to rounding of number to the nearest decimal place or to adjustable decimal places.
Someone has already shared this function in the comments to the CodeProject copy of this post. Enjoy
EX:
Round(1.234,2) = 1.23
Round(1.234,0) = 1.0
Round(123.4,-1) = 120.0