/*
  Expression tree, second version will make more aggressive use of
  inheritance.  That is, it tries to make maximum use of oop.
*/

using System;

public interface expr    // abstract interface for the expression class
{
   int eval();
   void print();
}

class intnode : expr  // integer expreesion
{
   int val;
   public intnode(int v) {val = v; }
   public int eval() { return val; }
   public void print() { Console.Write(val); }
} // intnode

class plusnode : expr // + operator expression
{
   expr left, right; // type of subtrees is "expr", not "node"!
   public plusnode(expr l, expr r) { left=l;  right=r; }
   public int eval()   {  return left.eval() + right.eval(); }
   public void print() 
   {
	Console.Write("(+ ");
	left.print(); Console.Write(" ");
	right.print(); 
        Console.Write(")");
   }
} // plusnode

class timesnode : expr // * operator expression
{
   expr left, right; // type of subtrees is "expr", not "node"!
   public timesnode(expr l, expr r) { left=l;  right=r; }
   public int eval()   {  return left.eval() * right.eval(); }
   public void print() 
   {
	Console.Write("(* ");
	left.print(); Console.Write(" ");
	right.print(); 
        Console.Write(")");
   }
} // timesnode