Question

I am doing my assignment in which I have to modify my previous task (which is prefix expression tree which takes expression and give result)

+ OR
* AND
- NOT

Now I have to make it Logic expression tree which will perform AND OR and NOT operations

char input;
    cin.get(input);

    if((input == '+')||(input == '-')||(input == '*'))
        {
        p = new ExprTreeNode(input,NULL,NULL);
         buildSub(p->left);
         buildSub(p->right);
      }
      else if(isdigit(input))
        {     //create a new node
            p = new ExprTreeNode(input,NULL,NULL);
        }
        else
      {
        cout <<" invalid expression exiting..." <<endl;
         exit (1);
       }

above code reads expression and makes tree using recursion…

I am confused how I can add unary operator that is NOT…
after that I have to evaluate expression

int answer;
    switch (p->dataItem){

        case '*':
            // AND
        case'+':
            // OR

        case '-':
            // Reverse

        default:
            answer = (p->dataItem-'0');
            break;
    }
    return answer;

p is ExprTreeNode

// Data members
        char dataItem;          // Expression tree data item
        ExprTreeNode *left,     // Pointer to the left child
                     *right;    // Pointer to the right child

Answer 1

I’d say you want to do the following:

if ((input == '+') || (input == '*'))
{
  p = new ExprTreeNode(input,NULL,NULL);
  buildSub(p->left);
  buildSub(p->right);
}
else if (input == '-')
{
  p = new ExprTreeNode(input, NULL, NULL);
  buildSub(p->left);
}
else if(isdigit(input))
{     //create a new node
  p = new ExprTreeNode(input,NULL,NULL);
}
else
{
  cout <<" invalid expression exiting..." <<endl;
  exit (1);
}

Edit:
Then, the evaluation routine could work like this:

bool ExprTreeNode::evaluate() {
  switch (dataItem) {
    case '+':
      return left->evaluate() || right->evaluate();
    case '*':
      return left->evaluate() && right->evaluate();
    case '-':
      return !left->evaluate();
    case '0':
      return false;
    default:
      return true;
  }
}