On Thu, 2021-10-14 at 15:20 +0000, frijolithedog 1 via Gcc-help wrote:
> I am having a C programing problem where <= is interpreted as < when
> using GCC 11.2.0
>
> I was debugging a larger program which I broke down into smaller
> sections of code and I noticed
> the following code was not working correctly:
>
> #include <stdio.h>
> #include <math.h>
> #include <float.h>
>
> int main(void)
> {
> float n, step;
>
> step = 0.1;
>
> for (n = 2; n <= 10; n = n + step )
> printf("%3.4f\n", n ); /* This stops
> at 9.9000 and not at 10.0000 */
>
> }
>
> I tried the above code only using the following include statement
> #include <stdio.h>
> but the result was the same.
It's because 0.1 is not something can be represented precisely using
float: it's binary representation is infinite. The float-type value
closet to 0.1 is 0.100000001490116119384765625, which is slightly larger
than 0.1.
Generally you shouldn't use a floating-point value as a loop iterator
unless you really know what you are doing.
--
Xi Ruoyao <xry111@xxxxxxxxxxxxxxxx>
School of Aerospace Science and Technology, Xidian University
