Check out example codes for "preorder traversal". It will help you in understanding the concepts better.

Code Example 1

``````#include <iostream>
using namespace std;

class node{
public:
int data;
node* left;
node* right;

node(int d){
data = d;
left = NULL;
right = NULL;
}
};

node* buildTree(){
int d;
cin>>d;

if(d==-1){
return NULL;	//to attach a NULL pointer[in case of no child] enter -1
}
node * root = new node(d);
root->left = buildTree();
root->right = buildTree();
return root;
}

//REQUIRED FUNCTION: Inorder Traversal

void printIn(node*root){
if(root==NULL){
return;
}
//Otherwise Left Root Right
printIn(root->left);
cout<<root->data<<" ";
printIn(root->right);
}

int main(){
node* root = buildTree();
printIn(root);

return 0;
}

//SAMPLE INPUT TO RUN THE CODE ON ANY ONLINE IDE:
//8 10 1 -1 -1 6 9 -1 -1 7 -1 -1 3 -1 14 13 -1 -1 -1``````

Code Example 2

``````// C program for different tree traversals
#include <iostream>
using namespace std;

/* A binary tree node has data, pointer to left child
and a pointer to right child */
struct Node
{
int data;
struct Node* left, *right;
Node(int data)
{
this->data = data;
left = right = NULL;
}
};

/* Given a binary tree, print its nodes according to the
"bottom-up" postorder traversal. */
void printPostorder(struct Node* node)
{
if (node == NULL)
return;

// first recur on left subtree
printPostorder(node->left);

// then recur on right subtree
printPostorder(node->right);

// now deal with the node
cout << node->data << " ";
}

/* Given a binary tree, print its nodes in inorder*/
void printInorder(struct Node* node)
{
if (node == NULL)
return;

/* first recur on left child */
printInorder(node->left);

/* then print the data of node */
cout << node->data << " ";

/* now recur on right child */
printInorder(node->right);
}

/* Given a binary tree, print its nodes in preorder*/
void printPreorder(struct Node* node)
{
if (node == NULL)
return;

/* first print data of node */
cout << node->data << " ";

/* then recur on left sutree */
printPreorder(node->left);

/* now recur on right subtree */
printPreorder(node->right);
}

/* Driver program to test above functions*/
int main()
{
struct Node *root = new Node(1);
root->left             = new Node(2);
root->right         = new Node(3);
root->left->left     = new Node(4);
root->left->right = new Node(5);

cout << "\nPreorder traversal of binary tree is \n";
printPreorder(root);

cout << "\nInorder traversal of binary tree is \n";
printInorder(root);

cout << "\nPostorder traversal of binary tree is \n";
printPostorder(root);

return 0;
}``````

Code Example 3

``````// C program for different tree traversals
#include <stdio.h>
#include <stdlib.h>

/* A binary tree node has data, pointer to left child
and a pointer to right child */
struct node
{
int data;
struct node* left;
struct node* right;
};

/* Helper function that allocates a new node with the
given data and NULL left and right pointers. */
struct node* newNode(int data)
{
struct node* node = (struct node*)
malloc(sizeof(struct node));
node->data = data;
node->left = NULL;
node->right = NULL;

return(node);
}

/* Given a binary tree, print its nodes according to the
"bottom-up" postorder traversal. */
void printPostorder(struct node* node)
{
if (node == NULL)
return;

// first recur on left subtree
printPostorder(node->left);

// then recur on right subtree
printPostorder(node->right);

// now deal with the node
printf("%d ", node->data);
}

/* Given a binary tree, print its nodes in inorder*/
void printInorder(struct node* node)
{
if (node == NULL)
return;

/* first recur on left child */
printInorder(node->left);

/* then print the data of node */
printf("%d ", node->data);

/* now recur on right child */
printInorder(node->right);
}

/* Given a binary tree, print its nodes in preorder*/
void printPreorder(struct node* node)
{
if (node == NULL)
return;

/* first print data of node */
printf("%d ", node->data);

/* then recur on left sutree */
printPreorder(node->left);

/* now recur on right subtree */
printPreorder(node->right);
}

/* Driver program to test above functions*/
int main()
{
struct node *root  = newNode(1);
root->left             = newNode(2);
root->right           = newNode(3);
root->left->left     = newNode(4);
root->left->right   = newNode(5);

printf("\nPreorder traversal of binary tree is \n");
printPreorder(root);

printf("\nInorder traversal of binary tree is \n");
printInorder(root);

printf("\nPostorder traversal of binary tree is \n");
printPostorder(root);

getchar();
return 0;
}``````

Code Example 4

``````/* Given a binary tree, print its nodes according to the
"bottom-up" postorder traversal. */
void printPostorder(struct Node* node)
{
if (node == NULL)
return;

// first recur on left subtree
printPostorder(node->left);

// then recur on right subtree
printPostorder(node->right);

// now deal with the node
cout << node->data << " ";
}``````

Learn ReactJs, React Native from akashmittal.com