Double value is rounded to unexpected value: 2.5 -> 2 instead of 3

[Ali Çehreli via Digitalmars-d-learn]

On 07/07/2017 11:29 AM, alex_ca wrote:

 > input 2.5 10 10
 > stitches: 2.5 -> 2
 > I expect: 3

That's because what is printed as 2.5 is actually a little less than 
that. (Try printing with a format string like "%.20f".)

The common way of dealing with this issue is to add 0.5 before the 
conversion:

import std.stdio;
import std.conv;

void main() {
     for (double d = 1; d < 2; d += 0.1) {
         writefln("%s (%.20f): %s", d, d, (d + 0.5).to!int);
     }
}

1 (1.00000000000000000000): 1
1.1 (1.10000000000000008882): 1
1.2 (1.20000000000000017764): 1
1.3 (1.30000000000000026645): 1
1.4 (1.40000000000000035527): 1
1.5 (1.50000000000000044409): 2
1.6 (1.60000000000000053291): 2
1.7 (1.70000000000000062172): 2
1.8 (1.80000000000000071054): 2
1.9 (1.90000000000000079936): 2

Ali