# Some letters get deciphered well, some don't, why?

Tell us what’s happening:
Describe your issue in detail here.
For instance, the letter E should turn to R, but it turns to an S, while R should, and turns to E. This is my second time writing here, so sorry in advance if I miss any important information here.

``````  **Your code so far**
``````
``````
function rot13(str) {
let finalStr = ''
let lettersArr = ['A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z']

for(let i = 0; i < str.length; i++) {
let oldIndex = lettersArr.indexOf(str[i]) + 1
let newIndex = oldIndex + 13;
let letter = ''

if(newIndex < 24) {
letter = lettersArr[newIndex]
} else if(newIndex > 24) {
newIndex -= 27
letter = lettersArr[newIndex]
}

if(str[i] === ' ') {
finalStr += ' '
} else {
finalStr += letter
}
}
console.log(finalStr)
}

rot13("SERR PBQR PNZC");
``````
``````  **Your browser information:**
``````

User Agent is: `Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/92.0.4515.131 Safari/537.36`

Challenge: Caesars Cipher

Take a closer look at the way `oldIndex` and `newIndex` is determined. Taking as an example case from the description, the indexes should be such that `A` should be encoded as `N`. Is that what happens here?

1 Like

Yup, the index of A is 1 (Yes arrays are zero indexed, but I added one to the index) so adding 13 will make it the letter at the 14th index, N, and vice versa, but for some reason N turns to A, but A doesn’t turn to N

No, the index of A is 0. It is the 1st element in the array but you cannot arbitrarily change to one based indexing. Tdat’s not how Javascript works.

To decode a letter you add 13. But sometimes adding 13 makes your index bigger than the number of elements in the array

What is the biggest possible index value in the array? Look carefully. Double check your count.

Spaces are not the only charcters you should leave unmodified.

Logging is not the same as returning.

As for the first part, for some reason 27 is the number that worked for me, I tried 24, which I thought would work, alongside other numbers and none of them gave good results, 15 (the letter O) plus 13 + 1 (the one I added) = 29 - 27 = 2, which is the letter B, the correct letter, this is basically the idea for indexes above 11. As for the spaces, it was more like a test, I was gonna finish it after I finish the deciphering part. And I was still using console.log instead of return as there was no way the current code would pass the tests, when it does I usually insert the return statement.

And thanks for explaining the index part, that’s new info to me. And thanks for spending time to explain the situation to me, I really appreciate that.

It looks like the +1 is making a mess of your arithmetic.

It could be, it was supposed to make the array non 0 indexed, but that seems to be impossible. Thanks for pointing that out!

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