Incrementing by < 1 in Javascript

Question

I've just been experimenting with for loops and noticed this when I changed the increment value to i += 0.1.

for (i = 0; i < 100; i += 0.1) {
    console.log(i);
}

In the console it returns

0
0.1
0.2
0.30000000000000004
0.4
0.5
0.6
0.7
0.7999999999999999
0.8999999999999999
0.9999999999999999

By the time you reach 100

99.69999999999861
99.7999999999986
99.8999999999986
99.9999999999986

What is the reason behind this? I imagine this would be frustrating if you are trying to search for a number. Is there a way to round to the nearest 10th? I know how to round with Math.floor, ~~, a | 0, but only to the nearest whole integer.

What is your real problem? and please read [floating-point tag kiwi](http://stackoverflow.com/tags/floating-point/info) — Bryan Chen, Dec 20 '16 at 00:19
First I've ever heard of 'floating point precision'. Thanks. — var name, Dec 20 '16 at 00:42
[This](http://stackoverflow.com/questions/40737008/floating-point-arithmetic-summation-versus-multiplication-of-error/) may help. — Rick Regan, Dec 20 '16 at 01:48

score 1 · Answer 1 · answered Dec 20 '16 at 00:34

1

I guess you are looking for something like this:

for (i = 0; i < 100; i += 0.1) {
    console.log(Math.round(i * 100) / 100);
}

answered Dec 20 '16 at 00:34

Pritam Banerjee

15,297
10
71
92

score 0 · Answer 2 · answered Dec 20 '16 at 00:29

0

Simple solution: Multiply by ten, add one, divide by ten.

for (var i = 0; i < 100; i = (i * 10 + 1) / 10) {
  console.log(i);
}

for (var i = 0; i < 100; i = (i * 10 + 1) / 10) {
      console.log(i);
    }

answered Dec 20 '16 at 00:29

Kyle Lin

786
6
16

Multiplying an imprecise value by 10 doesn't make it more precise. Better avoid floating point calculation as far as possible. `for (var i = 0; i < 1000; i++) { console.log(i / 10.0); }` – Roland Illig Dec 20 '16 at 00:37
You are not multiplying an "imprecise" floating point value by 10, but rather multiplying an integer by 10 and adding 1 and finally dividing by 10, to avoid the alternative, which is adding 0.1. With the former, you are performing integer addition and then dividing by ten to produce a float (which is precise enough for the purpose of answering this question). With latter, you are directly adding floats, which is not precise enought. – Kyle Lin Dec 20 '16 at 00:53

Incrementing by < 1 in Javascript

2 Answers2