Question

At the consturctor Node = new Node[numberOfNodes]; and Edge = new Edge[numberOfEdges]; gives identifier error? what’s the wrong with it ?

typedef struct node
{
 int id;
 int x;
 int y;
} Node;

typedef struct edge
{
 int id;
 Node node1;
 Node node2;
} Edge;

class graph
{
private:
 int numberOfNodes;
 int numberOfEdges;
 int *Node;
 int *Edge;

public:
 graph(int nodes, int edges)
 {
  numberOfNodes = nodes;
  numberOfEdges = edges;
  Node = new Node[numberOfNodes];
  Edge = new Edge[numberOfEdges];
 }

Answer 1

You have various variable name conflicts, including a conflict between your variable declaration int* Node, and the typedef Node. Also, you declare your array of nodes as type int* when it should be type Node*. You do the same with Edge. Try the following instead:

class graph
{
    private:
    int numberOfNodes;
    int numberOfEdges;
    Node* nodes_;
    Edge* edges_;

    public:

    graph(int num_nodes, int num_edges)
    {
        numberOfNodes = num_nodes;
        numberOfEdges = num_edges;
        nodes_ = new Node[numberOfNodes];
        edges_ = new Edge[numberOfEdges];
    }
};

Also, just for the future, the typedef struct { } idiom is really unnecessary in C++. It’s main purpose was so that C programmers wouldn’t need to constantly have to prefix their struct variables with the word struct. But in C++ this isn’t necessary, so there’s generally no real reason to say typedef struct node { ... } Node; when you can just say struct Node { ... };. See here for more information.