Simple encryption of a String in Java

Question

I want to write a program which will take a String and add 2 to every character of the String this was quite simple Here is my code. Example:-

String str="ZAP YES";
nstr="BCR AGU" //note Z=B and Y=A

String str=sc.nextLine();
String nstr=""    
for(int i=0;i<str.length();i++)
    {
        char ch=sc.charAt(i);
        if(ch!=' ')
        {
            if(ch=='Z')
                ch='B';
            else if(ch=='Y')
                ch='A';
            else
                ch=ch+2;
        }
        nstr=nstr+ch;
    }

Now I want to increase every character by n(instead of 2) and this really I could not solve.

I might think of using n%26 ,and use a loop for conditions but I was not able to solve it how to implement that.

Think about what happens if you have ch as 'z'? What happens if ascii char value of your character is 256? — SMA
– SMA, Commented Oct 11, 2017 at 15:58
n is a variable as in first case it is 2 now it is decided at runtime. — quadgen
– quadgen, Commented Oct 11, 2017 at 16:00
Note it may be assumed that the input string contains only spaces and Characters from Capital "A" to "Z". — quadgen
– quadgen, Commented Oct 11, 2017 at 16:02
since ASCII 'Z' is 90, just test your char if it's > 90 and if so subtract 26 — rguessford
– rguessford, Commented Oct 11, 2017 at 16:03

Mureinik · Accepted Answer · 2018-12-25 06:41:55Z

3

You have the right idea with using % 26. The missing piece is that your range isn't zero-based. You can simulate a zero-based range by subtracting 'A' (i..e, treating 'A' as 0, 'B' as 1, etc), and then readding it:

for (int i = 0; i < str.length(); i++) {
    char ch = str.charAt(i);
    if (ch != ' ') {
        ch = (char)((ch - 'A' + n) % 26 + 'A');
    }

    nstr += ch;
}

edited Dec 25, 2018 at 6:41

answered Oct 11, 2017 at 16:05

Mureinik

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2 Comments

quadgen Over a year ago

Just compiled your code and it worked as perfect as could thanks.

quadgen Over a year ago

Can Accept your answer in 2 minutes and said by SO

Oneiros · Accepted Answer · 2017-10-11 16:07:05Z

2

You have to:

Take your character and remap it to a 0-26 index
Add your increment to that index
Apply a 26 mod to the result
Remap the index back again to ASCII

Example:

public static char increment(char c, int n) {
   return (char) (((c - 'A') + n) % 26 + 'A');
}

public static void main(String[] args) {
  System.out.println(increment('Z', 1)); // returns 'A'
  System.out.println(increment('Z', 2)); // returns 'B'
}

answered Oct 11, 2017 at 16:07

Oneiros

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2 Comments

quadgen Over a year ago

You are a minute late sir can't accept your answer but it helped me and therefore a +1 by me.

Oneiros Over a year ago

ahah next time i’ll post code first and edit with comments later :) happy coding!

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