Rounding floating point program

Question

I'm trying to write a C program to find the smallest positive integer x so that (1/x) * x is not equal to 1, using single precision. And I do it again with double precision. I know that the x for single precision is 41, however when I test it by writing C code, I still get 1.00000

This is my test code

int main()
{
    float x = 41;
    float div = 1/x;
    float test = div * x;

    printf("%f\n", test);
}

I get 1.0000 instead of a 0.999999

please see docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html - they are just a representation of a number — Ed Heal
– Ed Heal, Commented Sep 29, 2015 at 19:33
The smallest positive integer is 1. (1/1) * 1 = 1. Why would x/x ever not be one for a real number other than 0? — Dark Squirtings
– Dark Squirtings, Commented Sep 29, 2015 at 19:36
@EdHeal in that case the document you posted is a must read :-) — sidyll
– sidyll, Commented Sep 29, 2015 at 19:38

R Sahu · Accepted Answer · 2015-09-29 19:44:30Z

1

You are not seeing the problem using

printf("%f\n", test);

since the default precision used by printf for floating point numbers is 6. If you increase the precision to 10, you will see that the number is not 1.0.

printf("%.10f\n", test);

prints 0.9999999404 for me.

answered Sep 29, 2015 at 19:44

R Sahu

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