import java.util.Scanner;

class Atoi
{
   /* ---
      parseInt(s): Ascii to Integer conversion function
      --- */
   private static int myParseInt(String s)
   {
      int startpos, sign;
      int value;
      char next_digit;
      int  value_of_digit;
      int i;

      /* -------
         Convert string to two's compl. representation
         ------- */
      if (s.charAt(0) == '-')
       { sign = -1;
         startpos = 1;
       }
      else
       { sign = 1;
         startpos = 0;
       }

      /* ==============================================================
         E.g.: s = "123"

            i      next_digit  val_of_digit    partial result
          ---------------------------------------
	                                        value =  0
            0         '1'        '1'-'0'=1      value =  0*10 + 1 =   1
            1         '2'        '2'-'0'=2      value =  1*10 + 2 =  12
            2         '3'        '3'-'0'=3      value = 12*10 + 3 = 123
         ============================================================== */
      value = 0;
      for (i = startpos; i < s.length(); i++)
      { 
         next_digit = s.charAt(i);
	 value_of_digit = (int) next_digit - (int) '0';

         value = 10*value + value_of_digit;
      }

      if (sign == -1)
         value = -value;

      return(value);
   }

   public static void main(String[] args) 
   {
      Scanner in = new Scanner(System.in);

      String s1, s2;
      int i1, i2;

      System.out.print("Enter an integer (string) s1: ");
      s1 = in.next();

      System.out.print("Enter an integer (string) s2: ");
      s2 = in.next();

      System.out.println("s1 + s2 = " + (s1+s2) );
      System.out.println();

      i1 = myParseInt(s1);  // Same effect as: i1 = Integer.parseInt(s1); !!!!
      i2 = myParseInt(s2);  // Same effect as: i2 = Integer.parseInt(s2);
      System.out.println("i1 + i2 = " + (i1+i2) );
   }
}