[FIXED] why does there is no update in Node *root?

Issue

This is a very simple example for inserting a number.

typedef struct node {
    int data;
    struct node *left, *right;

} node;

node * newNode(int val) {
    node* n = malloc(sizeof(node));
    n->data=val;
    n->left=NULL;
    n->right=NULL;
    return n; }

void insert(node* node, int key) {    
    if (node == NULL)
        node = newNode(key);
}

int main() {
    node *root = NULL;
    insert(root, 5);

    printf("%d\n", root->data);

    return 0;
}

The problem is, Why does the printf print nothing when I insert 5 in root?

Solution

In C all arguments are passed by value. That means the value is copied into the argument variable, and when you do the assignment node = newNode(key); you only assign to the local node variable.

There are two solutions to this problem:

1. Return the new node instead:

   node* insert(node* the_node, int key) {    
       if (the_node == NULL)
           the_node = newNode(key);
       return the_node;
   }
   
   ...
   
   root = insert(root, 5);
   

2. Emulate pass by reference, which can be done by passing a pointer to the variable using the address-of operator &:

   void insert(node** the_node, int key) {    
       if (*the_node == NULL)
           *the_node = newNode(key);
   }
   
   ...
   
   insert(&root, 5);
   

Answered By - Some programmer dude

Answer Checked By - Senaida (PHPFixing Volunteer)