Q.9 - Write a program to demonstrate the addition of two strings digitwise.

public class StringAdd{
 public static void main(String args[]){
  String a = "9999999999999999999";
  String b = "2222222222222222222";
  int c1[] = new int[b.length()];
  try
  {
   for(int i=0;i<a.length() && i<b.length();i++)
    c1[i] = Integer.parseInt(String.valueOf(a.charAt(i))) + Integer.parseInt(String.valueOf(b.charAt(i)));
  }

  catch(NumberFormatException e)
  {
   System.out.println("Please give strings containing numeric characters only");
   return;
  }
  System.out.println(new StringAdd().toString(c1));
 }

 //Override toString() method to convert int array to string
 public String toString(int arr[]){
  String str="";
  for(int k:arr)
   str = str + Integer.toString(k);
  return str;
 }
}