Can't work why?

Question

import java.util.Scanner;
public class Program
{
public static void main(String[] args) {
Scanner sc=new Scanner(System.in);
String letter=sc.nextLine(); String[]num={"0","1","2","3","4","5","6","7","8","9"};
String[]word={"zero","one","two","three","four","five","six","seven","eight","nine"};
for(int i=0;i<=num.length-1;i++){

String letter1=letter.replaceAll(num[i],word[i]);}
System.out.println(letter1);

}
}

Answer 1

'letter1' doesn't exist outside the for-loop.
Also, you should assign to 'letter1' from the already modified string (letter1) , not the source (letter)

String letter1 = letter;
for(int i=0; i<n.length; i++){
letter1 = letter1.replace...
}

Answer 2

thank you