Java For loops and char arrays

Question

I am making a "Code Decoder" - So there are 3 lines, the first is the reference string, the second is jumbled, and then the third is calculated based on matching the first and second strings. Example:

THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG
UIFARVJDLACSPXOAGPYAKVNQTAPWFSAUIFAMB ZAEPH
XFABSFAWFSZACBEAQFPQMFAEPJOHAWFSZACBEAUIJOHTAIBAIB

What I'm doing is getting the 3 strings, converting them to char arrays, then looking through the first string, finding where it is in the array of the alphabet, then at that position I enter the letter from the second string on another array at the same place. Therefore, later, I can find a letter in the alphabet and get its corresponding letter in the second array.

Problem - nothing is inputting into the second array... It comes up empty.

Let me know if any clarification is needed.

    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    System.out.print("Enter First String:"); // First String
    String first_string = br.readLine();
    System.out.print("Enter Second String:"); // Second String 
    String second_string = br.readLine();
    System.out.print("Enter Third String:"); // Third String 
    String third_string = br.readLine();

    char[] first = first_string.toCharArray();
    char[] second = second_string.toCharArray();
    char[] third = third_string.toCharArray();
    char[] compare_a = {'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'}; //length = 26
    char[] compare_b = new char[26]; //length = 26

    for(int x =0; x < first.length ; x++){// going through first array
        char first_letter = first[x]; // gets letter from first string

        for(int z = 0; z < 26; z++){ // looks through alphabet for the position of the letter
            if(first_letter == compare_a[z]){ // if the letter is found at a certain position
                // System.out.println(first_letter + " = " + compare_a[z] + " " + compare_b[z]  + " " +  second[x]);
                compare_b[z] = second[x]; // insert into the same position on the second array
            }
        }
    }

    for(int t =0; t<26; t++){

        char m = compare_b[t];
        System.out.print(m); //Printing out array of new letters
    }
}

Note:

When I tried outputting the results to a string, it comes out correctly ---

   letters = letters + second[x];

It just doesn't go into the array...

Use debugger or add println statements to make sure your strings contain what you expect. — PM 77-1
– PM 77-1, Commented Jan 11, 2014 at 23:57
I did - and all the strings have what I want - but the "compare_b" array isn't including the new values. — Ds.109
– Ds.109, Commented Jan 11, 2014 at 23:59
Step through your code with the debugger. Does the if statement evaluate to false all the time? — SirRichie
– SirRichie, Commented Jan 12, 2014 at 0:00
Actually you don't need to convert string to char array; you can determine position of a character using charAt() method — user2672373
– user2672373, Commented Jan 12, 2014 at 0:00
Did the debug line (commented out) inside the if-statement show what you would expect while stepping through the code in the debugger? — nalyd88
– nalyd88, Commented Jan 12, 2014 at 0:02

MariuszS · Accepted Answer · 2014-01-12 00:21:25Z

1

Bug

Should be

compare_b[z] = second[z];

but is

compare_b[z] = second[x];

Fixed code

public static void main(String[] args) {

        String first_string = "THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG";
        String second_string = "UIFARVJDLACSPXOAGPYAKVNQTAPWFSAUIFAMB ZAEPH";
        String third_string = "XFABSFAWFSZACBEAQFPQMFAEPJOHAWFSZACBEAUIJOHTAIBAIB";

        char[] first = first_string.toCharArray();
        char[] second = second_string.toCharArray();
        char[] third = third_string.toCharArray();
        char[] compare_a = {'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'}; //length = 26
        char[] compare_b = new char[26]; //length = 26

        for (int x = 0; x < first.length; x++) {// going through first array
            char first_letter = first[x]; // gets letter from first string

            for (int z = 0; z < 26; z++) { // looks through alphabet for the position of the letter
                if (first_letter == compare_a[z]) { // if the letter is found at a certain position
                    // System.out.println(first_letter + " = " + compare_a[z] + " " + compare_b[z]  + " " +  second[x]);
                    compare_b[z] = second[z]; // insert into the same position on the second array
                }
            }
        }

        for (int t = 0; t < 26; t++) {

            char m = compare_b[t];
            System.out.print(m); //Printing out array of new letters
        }
    }

Fixed result is

UIFARVJDLACSPXOAGPYAKVNQTA

edited Jan 12, 2014 at 0:21

answered Jan 12, 2014 at 0:12

MariuszS

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4 Comments

Ds.109 Over a year ago

Yes - I was fiddling and made it come empty for a second ... However it shouldn't because when I output this: System.out.println(first_letter + " = " + compare_a[z] + " " + compare_b[z] + " " + second[x]); The proper values are there... but they don't input to the compare_b[] array

MariuszS Over a year ago

@Ds.109 compare_b[z] = second[z]; <- change z with x :)

Ds.109 Over a year ago

That's great that it inputs into the array! But I want it to input the letter in the same position as in the alphabet --- So, the first U should be in the 19th spot in the array.. so i can match it with the alphabet.

Ds.109 Over a year ago

Nevermind -it worked ! I used x and it worked for some reason :)

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