Trying to write a simple compiler in java (I am using notepad++)

Question

My question is how would I write a simple compiler ,that is like the compilers used in fax machines, that would convert something like aaaavvvvvddddddddddd to 4a5vBd.

Also, I get to "Assume" that any string entered will not contain uppercase letters and no numbers, and that any string will contain less than 61 of any type of character so, I get to assume no one will put in 64 continues a's in my program.

This is as far as I gotten

import java.util.*;
public class Program4
{

    public static void main(String[] args)
    {
        Scanner scan = new Scanner(System.in);
        int n;
        char cn;
        String word;
        String numChars = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";

        System.out.println("Hello, please enter a string");
        word = scan.nextln();

        if(n <= 61)
        {
        int n = ?;
        cn = numChars.charAt(n);
        }
    }
}

I assume I need to use a loop, but I don't know what I should use to count the repeating letters and then tell how many letters of that type are in a row. Now I am only asking for advice and not so much for code, because I want to do it but, as a beginner my Java "Vocabulary" isn't very big right now.

Any advice/ tips would be greatly appreciated.

Sincerely, Mr.Trips

Well I am back and it appears my code here likes to only print out 147. No matter what I type in I will always get 147. I have tried to hand trace all my variables, but when I do it I get exactly what I want, and I must have some error in my logic. Any thoughts?

import java.util.*;    
public class Program4
{
    public static void main(String[] args)
    {

        Scanner scan = new Scanner(System.in);
        int n = 0;
        int s = 0;
        char a;
        char b;
        char c;
        String word;
        String numChars = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";

        System.out.println("Please enter a string");
        word = scan.nextLine();


        while (n < word.length()) 
        {
            a = word.charAt(n);
            b = a;
            n = n ++;
            a = word.charAt(n);

            if (a == b)
            {
                    s = (s + 1) ; 
            }
            else if (a != b);
            {
                c = numChars.charAt(s);
                System.out.print(b + c);
                s = 0;
                c = 0;
                break;

            }
        }
    }
}

Thank you again!

Answer 1

Since you don't want code this is logically how to do it. You are right you should loop through the string for each char. Store the last char in a variable and keep a counter variable. Compare current char to last char if it is equal then increment the counter. As soon as it is not equal to the last char then add counter + last char to result string and reset counter variable. Each iteration update last char variable.