Imitating binary search trees with array

I've been having logic issues with this code; for some reason whenever I reach a leaf on the tree, it skips ahead and the input doesn't come out correctly. I feel like it's something very simple I'm just overlooking, and I'm going to feel very stupid if that's the case... but I'm completely lost at this point.

 ``123456789101112131415161718192021222324252627282930313233343536373839404142434445464748`` ``````#include using namespace std; tree[100]; void insert(int n) { int index = 1; if (tree[index] == -1) //insert the value into the current index { tree[index] = n; } else if (tree[index] != -1) //if index is already filled { if (n < tree[index]) //value is less than root value { while (tree[index] != -1) { index *= 2; } if (tree[index] == -1) tree[index] = n; else { tree[index] = n; } } else if (n > tree[index]) //value is greater than root value { while(tree[index] != -1) { index *= 2; index += 1; } if (tree[index] == -1) tree[index] = n; else { tree[index] = n; } } } }``````

This is the input in the main function:

 ``12345678910111213141516171819202122232425`` ``````int main() { //-1 = NULL for (int i = 0; i <= 100; i++) tree[i] = -1; insert(5); insert(8); insert(3); insert(1); insert(4); insert(9); insert(18); insert(20); insert(19); insert(2); cout << "Tree Output: [ "; for (int j= 0; j< 100; j++) cout << tree[j] << " "; cout << "]" << endl << endl; return 0; }``````

The output looks something like this:

 ```Tree Output: [ -1 5 3 8 1 -1 -1 9 4 -1 -1 -1 -1 -1 -1 18 2 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 20 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 19 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 ] Press any key to continue . . .```

The output is close, but the 4, 2 and 19 are off; the 4 should be in index 5, the 2 should be in index 9, and the 19 should be in index 62. Everything else is properly placed.
Hi there,

Unfortunately I'm not immediately able to pinpoint the issue as I have never implemented a binary search tree myself. Nonetheless I want to point out one or two things in your code:

 ``12345678910111213141516171819202122232425262728293031`` ``````if (tree[index] == -1) //insert the value into the current index { tree[index] = n; } else if (tree[index] != -1) //Just use regular else, intent is clearer { if (n < tree[index]) //value is less than root value { while (tree[index] != -1) { index *= 2; } if (tree[index] == -1) //this if and else do exactly the same tree[index] = n; else tree[index] = n; } else if (n > tree[index]) { while(tree[index] != -1) { index *= 2; index += 1; } if (tree[index] == -1) //this if and else do exactly the same tree[index] = n; else tree[index] = n; } //you have defined a case for n>, n<, but what if n==tree[index]? }``````

Now, I don't know if this is for an assignment or how advanced your c++ knowledge is, but if I were to implement one the least I would do is to create a Node-struct. I don't think I would use an array either, because at some point these lines `index *= 2;` are going to go out of the bounds of the array (causing a segfault), especially if your tree is unbalanced (or whatever the official term for that is).

As a quick mock up:

 ``12345678910111213141516171819202122232425262728293031323334353637383940`` ``````template struct node { node* left_child; node* right_child; node* parent; T value; }; template class binary_search_tree { public: void insert(const T element) { insert_recursively(element, root) } private: node root; void insert_recursively(const T& element, node* node_ptr) { if (node_ptr.value < element) { insert_recursively(element, node_ptr->left_child); } else if (node_ptr.value > element) { insert_recursively(element, node_ptr->right_child); } else { node* n = new node(); n.value = element; //make n's parent the node_ptr's parent //make node_ptr's parent n } } };``````

Again, this is just a quick mock-up, I haven't put much thought into it and it probably won't compile. I just wanted to make my point clear about using a node-struct and making inserting recursive.

Hopefully that helps a little, otherwise just say so and I'm sure one of the exerts on this forum will be happy to give you some better feedback.

All the best,
NwN
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