Making the leap from Java to C++

Question

As the topic says I'm very new to c++, but I have some experience with java. To start learning c++ I had the (not very original) idea of making a simple command line calculator. What I'm trying to do is store the numbers and operators in a binary tree.

#include <iostream>
using namespace std;

class Node
{
  bool leaf;
  double num;
  char oper;
  Node* pLNode;
  Node* pRNode;

public:

  Node(double n)
  {
    num = n;
    leaf = true;
    pLNode = 0;
    pRNode = 0;
  }

  Node(char o, Node lNode, Node rNode)
  {
    oper = o;
    pLNode = &lNode;
    pRNode = &rNode;
    leaf = false;
  }

  bool isLeaf()
  {
    return leaf;
  }

  double getNumber()
  {
    return num;
  }

  char getOperator()
  {
    return oper;
  }

  Node* getLeftNodePointer()
  {
    return pLNode;
  }

  Node* getRightNodePointer()
  {
    return pRNode;
  }

  //debug function
  void dump()
  {
    cout << endl << "**** Node Dump ****" << endl;
    cout << "oper: " << oper << endl;
    cout << "num: " << num << endl;
    cout << "leaf: " << leaf << endl;
    cout << "*******************" << endl << endl;
  }

};

class CalcTree
{
  Node* pRootNode;
  Node* pCurrentNode;
public:

  Node* getRootNodePointer()
  {
    return pRootNode;
  }

  Node* getCurrentNodePointer()
  {
    return pCurrentNode;
  }

  void setRootNode(Node node)
  {
    pRootNode = &node;
  }

  void setCurrentNode(Node node)
  {
    pCurrentNode = &node;
  }

  double calculateTree()
  {
    return calculateTree(pRootNode);
  }

private:

  double calculateTree(Node* nodePointer)
  {
    if(nodePointer->isLeaf())
    {
      return nodePointer->getNumber();
    }
    else
    {
      Node* leftNodePointer = nodePointer->getLeftNodePointer();
      Node* rightNodePointer = nodePointer->getRightNodePointer();
      char oper = nodePointer->getOperator();

      if(oper == '+')
      {
    return calculateTree(leftNodePointer) + calculateTree(rightNodePointer);
      }
      else if(oper == '-')
      {
    return calculateTree(leftNodePointer) - calculateTree(rightNodePointer);
      } 
      else if(oper == '*')
      {
    return calculateTree(leftNodePointer) * calculateTree(rightNodePointer);
      }
      else if(oper == '/')
      {
    return calculateTree(leftNodePointer) / calculateTree(rightNodePointer);
      }
    }
  }
};

int main(int argc, char* argv[])
{
  CalcTree tree;
  tree.setRootNode(Node('+', Node(1), Node(534)));
  cout << tree.calculateTree() << endl;
  return 0;
}

I've got a couple of questions about this code:

1. This compiles but does not do what's intended. It seems that after tree.setRootNode(Node('+', Node(1), Node(534))); in main, the rightnode is initialized properly but the leftnode isn't. Compiling and running this prints out 534 for me (gcc, freebsd). What is wrong here?

2. It seems in c++ people prefer to define members of a class outside the class, like

   class A { public: void member(); };

   A :: member(){std::cout << "Hello world" << std::endl;}

   why is that?

3. I'd very much like some pointers on c++ conventions (naming, indenting etc.)

4. I'm used to coding java with eclipse. Atm I'm using emacs for learning c++. Can someone advise me on a good (free) c++ ide, or should I stfu and stick with emacs like a real man? :)

Answer 1

• First, I can only recommend to have a look at the book "Accelerated C++". It will jump-start you into STL, and C++ style, and can save you a year of bad experiences. (There is quite an amount of extraordinary well written literature on C++ out there, if you decide to go deeper).

• C++ does not use automatic memory management on the heap. You are storing pointers to temporaries. Your program is incorrect as it tries to access destructed objects. Like it or not, you'll have to learn on object lifetime first. You can simplify a good part of this in simple cases by using value semantics (not storing pointers, but storing a copy of the object).

• Eclipse/CDT is reported to be quite OK on linux. On Windows you'll do easier with Microsoft Visual C++ Express Edition. When you've gotten into the basics, switching later will be no problem for you.

• Defining members outside of the class itself is preferred as we usually split header and implementation files. In the header you try not to expose any unnecessary information, and also to reduce code-size, it's a simple matter of compile time. But for many modern programming techniques (like using template meta-programming) this cannot be used, so quite some C++ code moves in the direction of inline definitions.