Not able to understand javascript behaviour

Question

I am trying to execute the following code

var n = 100;
var sum =0;
while(n>0)
{
sum = sum + n%10;
n = n/10;
}
console.log(sum);

The result should be 1 but javascript is returning

1.1111111111111112

Also, when I ran individual statements it is giving perfectly fine result, what could be the possible reason?

first iteration n = 100, second n = 10, 3rd n = 1, 4th n= 0.1, 5th n=0.01, until n is small enough to be equal to 0, at 1e-324 on my machine — Kaiido, Nov 14 '16 at 07:20
Why would you think that it should be 1? When `n` goes into decimal numbers `0.1%10 == 0.1`, `0.01%10 == 0.01` you get `n` back so as you add them to the previous sum you get `1.1111.....` Also you are lucky that at certain precision the value just becomes 0 as otherwise you would have an infinite loop — Patrick Evans, Nov 14 '16 at 07:20
`n%10` for numbers less than `10` is `n`. The numbers don't have to be integers for it to work (maybe they should? who knows) — apokryfos, Nov 14 '16 at 07:22

madhur · Answer 1 · 2016-11-14T07:48:00.983

7

The result it is giving is correct -

Lets go into while loop

For first iteration n=100 so n%10 = 0 and sum = 0, after first loop sum = 0 and n = 10

In second iteration n%10 = 0 and sum = 0, after second iteration sum = 0 and n = 1

For third iteration n%10 = 1 and sum =0, after third iteration sum = 1 and n = 0.1

For fourth iteration n%10 = 0.1 and sum = 1, after fourth iteration sum = 1.1 and n = 0.01

and so on so forth

finally the answer would be 1.1111111111....... tending to infinity so it becomes 1.1111111111111112

Hope this helps

EDIT

If you want final answer as 1, intialise n as 0.9(n = 0.9)

edited Nov 14 '16 at 07:48

answered Nov 14 '16 at 07:23

madhur

973
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Finally! someone has come up to present the fact that OP's expectation is incorrect, instead of just rounding a number down to a completely invalid value. Way to go! – Hanky Panky Nov 14 '16 at 07:33
while this anwer declares what happen, the op does not get what is requested, a result with one. – Nina Scholz Nov 14 '16 at 07:40
@NinaScholz Edited, getting final answer as 1 is just playing with numbers here and there – madhur Nov 14 '16 at 07:48

score 2 · Answer 2 · answered Nov 14 '16 at 07:23

No, the result won't be 1. Notice that your loop is dividing n by 10 every iteration, and that the continuing condition is n > 0, which will take many iterations till it happens:

n=100, n%10=0
n=10, n%10=0
n=1, n%10=1
n=0.1, n%10=0.1
n=0.01, n%10=0.01
...

So, the result is correct: 1.1111111... The 2 at the end is no more than a rounding decimal error (minimal).

Not able to understand javascript behaviour

2 Answers2