Why use printf %f for print 100.00100 results 100.000999?

Asked May 25 '18 at 10:36

Active May 25 '18 at 10:37

Viewed 53 times

I have this code:

#include  <stdio.h>

int main(void)
{
    float c = 100.001000;
    printf("%f\n",c);
    return 0;
}

But result is:

100.000999

Why this happen? Where is rule for this result in C standards?

edited May 25 '18 at 10:37

Biffen

asked May 25 '18 at 10:36

S.rah

1

In binary floating point, there's no such number as exactly 100.001. (Just as in decimal floating point, there's no such number as exactly 1/3.) – Steve Summit May 25 '18 at 10:52
As the constant `100.001000` is not exactly representable as a `double`, the closest alternative is used `100.00100000000000477...`. Yet this `double` constant fails to store exactly as a `float`. The closest is `100.00099945068359375` which when printed to 6 places after the `.` rounds , as text, to `100.000999` – chux - Reinstate Monica May 25 '18 at 11:07

0 Answers0