C++ Notes: Expression Tree Struct

This code is a typical non-OOP solution to the expression tree problem.

   //======================================= ExprNode
   struct ExprNode {
      char      op;    // one of +, -, *, /, #
      int       value; // integer value
      ExprNode* left;  // left subtree
      ExprNode* right; // right subtree
   };
   
   

   //======================================= eval
   int eval(ExprNode* x) {
      // Recursively evaluate expression tree
      // and return result.
      int result;
      switch (x->op) {
         case '+': result = eval(x->left) + eval(x->right);
                   break;
         case '-': result = eval(x->left) - eval(x->right);
                   break;
         // . . .
         case '#': result = x->value;  // an integer constant
      }
      return result;
   }

Solutions like this are quite adequate, however the idea of OOP programming is to bundle the constructors and methods with the data structure as shown in the next example.