CODEWITHSUNDEEP
javascriptarraysloopslogic
Urrby
Urrby

Reputation: 41

Repeat the alphabet

Im a beginner programmer and I know that this is probably an easy problem, Im having difficulty understanding the logic. Im working on a program that deciphers Caesars Cipher with ROT13 cipher. Its one of the tasks at FreeCodeCamp. But their solutions are quite hard for me to understand at my skill level, so I want to make it my own way. I managed to get it quite far but i stumbled upon a problem. Im working with arrays, and I will return the array with deciphered message. The output in this case should be [F, R, E, E, , C, O, D, E, , C, A, M, P], but instead I get [undefined, "R", undefined, undefined, undefined, "O", undefined, undefined, undefined, undefined, undefined, "P"]. I understand that I get undefined because j+13 is bigger than 26 in cases of undefined and there are only 26 letters in alphabet or in array. I cant figure out how to make, so that alphabet will repeat itself in the cases where j+13 > 26. Any tips would be really helpful

let str = "SERR PBQR PNZC";
        let strArr = str.split("");
        let alphabet = [];
        let tempArr = [];
        for (i = 65; i <= 90; i++){
            alphabet.push(String.fromCharCode(i))
        }
        for (i = 0; i < strArr.length; i++) {
            for (j = 0; j < alphabet.length; j++) {
                if (strArr[i] === alphabet[j]) {
                    tempArr.push(alphabet[j+13]);

                }

            }

        }
    console.log(tempArr);

Upvotes: 2

Views: 82

Answers (1)

Paul
Paul

Reputation: 141829

alphabet[j+13] is often undefined since j+13 is past the end of the alphabet whenever j >= 13. You can use the remainder operator % to effectively wrap around to the beginning of the array again instead of going past the end of it. Just change it to alphabet[(j+13)%26]:

let str = "SERR PBQR PNZC";
        let strArr = str.split("");
        let alphabet = [];
        let tempArr = [];
        for (i = 65; i <= 90; i++){
            alphabet.push(String.fromCharCode(i))
        }
        for (i = 0; i < strArr.length; i++) {
            for (j = 0; j < alphabet.length; j++) {
                if (strArr[i] === alphabet[j]) {
                    tempArr.push(alphabet[(j+13)%26]);

                }

            }

        }
    console.log(tempArr);

Upvotes: 1

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