Insertion failure in a Binary Search Tree

Question

Here is my code for the creation and insertion of the binary search tree

struct BTNode
{
    int info;
    struct BTNode *left, *right;
};

struct BTNode* create(int data)
{
    struct BTNode *root;
    struct BTNode *n = malloc(sizeof(struct BTNode));

    n->info = data;
    n->left = NULL;
    n->right = NULL;
    root = n;

    return(root);
}

struct BTNode* insert(struct BTNode *root, int data)
{
    struct BTNode *ptr;
    struct BTNode *n = malloc(sizeof(struct BTNode));
    if (n == NULL)
        printf("\nOUT OF MEMORY!\n");

    n->info = data;
    n->left = NULL;
    n->right = NULL;


    ptr = root;
    while (ptr != NULL){
        if (data < ptr->info){
            if (ptr->left == NULL)
            ptr->left = n;

            ptr = ptr->left;
        }
        else if (data > ptr->info){
            if (ptr->right == NULL)
            ptr->right = n;

            ptr = ptr->right;
        }
    }

    return(n);
}

and here is the main() function

int main()
{
    struct BTNode *root = NULL;
    int choice, data;

    printf("\nWrite the root data: ");
    scanf("%d", &data);
    root = create(data);

    while (1){
    printf("\n1.Insert 2.Preorder 3.Exit\n");
    scanf("%d", &choice);
    switch(choice){
        case 1:
        printf("\nWrite the data: ");
        scanf("%d", &data);
        insert(root, data);
        break;

I am able to create the root node but whenever I am trying to insert the data, I give my data and the compiler stops doing anything. Any idea why this is happening?

Answer 1

Your while() loop goes on forever because you keep going even after you find a place to insert the node:

while(ptr!=NULL){
    if(data<ptr->info){
        if(ptr->left==NULL)
        ptr->left=n;

        ptr=ptr->left;
    }
    else if(data>ptr->info){
        if(ptr->right==NULL)
        ptr->right=n;

        ptr=ptr->right;
    }
}

You need to break out of the while() loop after inserting the node:

while (ptr != NULL) {
    if (data < ptr->info) {
        if (ptr->left == NULL) {
            ptr->left = n;
            break;
        }


        ptr = ptr->left;
    } else if (data > ptr->info) {
        if (ptr->right == NULL) {
            ptr->right = n;
            break;
        }


        ptr = ptr->right;
    }
}

Also, bonus points for checking if malloc() fails

struct BTNode *n = malloc(sizeof(struct BTNode));
if (n == NULL)
    printf("\nOUT OF MEMORY!\n");

But negative points for simply continuing on anyway, you should exit the function if malloc() fails

struct BTNode *n = malloc(sizeof(struct BTNode));
if (n == NULL) {
    printf("\nOUT OF MEMORY!\n");
    return NULL:
}

And then of course, the code calling insert() should know what to do if insert() returns NULL.