Question

struct node{
  int element;
  node* left;
  node* right;
};

typedef node* SET;

void INSERT(int x, SET* A){
  node* pA = *A;
  if (pA == NULL){
    pA = new node;
    pA->element = x;
    pA->left = NULL;
    pA->right = NULL;
  }
  else{
    if (x < pA->element){
      INSERT(x,&(pA->left));
    }
    else if (x>pA->element){
      INSERT(x, &(pA->right));
    }
  }
}

int main(){
  node* A = NULL;
  INSERT(1,&A);
  cout <<A->element<<endl;
  return 0;
}

The Code above is a simple insertion method that will insert an element into the BST. I just keep getting segment default when I access A->element. Many Thanks from your answer.

Edit:

wow, this pointer stuff is really confusing. So when I do node* pA = *A, I thought I would create a pointer pointing to the location of A. Then when I do pA = new node, it would create a node object in the heap pointing by pA which is the same as A. Am I saying anything wrong?

Answer 1

Consider using C++ references.

References allow the A in INSERT and the A in main to represent the same data, reducing pointer confusion.

struct node{
  int element;
  node* left;
  node* right;
};

void INSERT(int x, node* &A){
  if (A == NULL){
    A = new node;
    A->element = x;
    A->left = NULL;
    A->right = NULL;
  }
  else{
    if (x < A->element){
      INSERT(x,&(A->left));
    }
    else if (x>A->element){
      INSERT(x, &(A->right));
    }
  }
}

int main(){
  node* A = NULL;
  INSERT(1,A);
  cout <<A->element<<endl;
  return 0;
}