Iterative Tree Traversals

The below functions assume that a stack of type pointer to Node is already created which supports push and pop operations.

Preorder Traversal :

void preorderTraversal(struct Node *ptr) {

    // A stack to keep track of visited nodes
    struct Stack s;
    
    // Iterate until pointer is not NULL or stack is not empty
    while (ptr != NULL || !isEmpty(s)) {
        if (ptr) {
            printf("%d\t", ptr -> data);
            // Push current node address to stack
            push(&s, p);
            ptr = ptr -> left;
        } else {
            ptr = pop(&s);
            ptr = ptr -> right;
        }
    }

}

Inorder Traversal :

void inorderTraversal(struct Node *ptr) {

    // A stack to keep track of visited nodes
    struct Stack s;
    
    // Iterate until pointer is not NULL or stack is not empty
    while (ptr != NULL || !isEmpty(s)) {
        if (ptr) {
            // Push current node address to stack
            push(&s, p);
            ptr = ptr -> left;
        } else {
            ptr = pop(&s);
            printf("%d\t", ptr -> data);
            ptr = ptr -> right;
        }
    }

}

Postorder Traversal :

void postorderTraversal(struct Node *ptr) {

    // A stack to keep track of visited nodes
    struct Stack s;
    
    // Iterate until pointer is not NULL or stack is not empty
    while (ptr != NULL || !isEmpty(s)) {
        if (ptr) {
            // Push current node address to stack
            push(&s, p);
            ptr = ptr -> left;
        } else {
            ptr = pop(&s);
            ptr = ptr -> right;
            printf("%d\t", ptr -> data);
        }
    }

}

Contributed by Nitin Ranganath