Inorder, Preorder and Postorder Successor and Predecessor Functions inC++

#include<iostream>
using namespace std;
struct node
{
    int data;
    struct node* left;
    struct node* right;
    struct node* next;
};
struct node* createnode(int x)
{
    struct node* new_node=new struct node;
    new_node->data=x;
    new_node->left=NULL;
    new_node->right=NULL;
    new_node->next=NULL;
    return new_node;
}
void inord_succ(struct node* root,struct node** prev)
{
    if(root)
    {
        inord_succ(root->left,prev);
        if(*prev!=NULL)
        {
            (*prev)->next = root;
            *prev = root;
        }
        else
        {
            *prev = root;
        }
        inord_succ(root->right,prev);
    }
}
void inord_pred(struct node* root,struct node** prev)
{
    if(root)
    {
        inord_pred(root->left,prev);
        root->next=*prev;
        *prev=root;
        inord_pred(root->right,prev);
    }
}
void preord_succ(struct node* root,struct node** prev)
{
    if(root)
    {
        if(*prev!=NULL)
        {
            (*prev)->next=root;
            *prev=root;
        }
        else
        {
            *prev=root;
        }
        preord_succ(root->left,prev);
        preord_succ(root->right,prev);
    }
}
void preord_pred(struct node* root,struct node** prev)
{
    if(root)
    {
        root->next=*prev;
        *prev=root;
        preord_pred(root->left,prev);
        preord_pred(root->right,prev);
    }
}
void postord_succ(struct node* root,struct node** prev)
{
    if(root)
    {
        postord_succ(root->left,prev);
        postord_succ(root->right,prev);
        if(*prev!=NULL)
        {
            (*prev)->next=root;
            *prev=root;
        }
        else
        {
            *prev=root;
        }
    }
}
void postord_pred(struct node* root,struct node** prev)
{
    if(root)
    {
        postord_pred(root->left,prev);
        postord_pred(root->right,prev);
        root->next=*prev;
        *prev=root;
    }
}
void inorder(struct node* root)
{
    if(root)
    {
 inorder(root->left);
 cout<<root->data<<" ";
 if(root->next)
 {
     cout<<root->next->data<<endl;
 }
 else
 {
     cout<<endl;
 }
 inorder(root->right);
    }
}
void preorder(struct node* root)
{
    if(root)
    {
        cout<<root->data<<" ";
        if(root->next)
        {
            cout<<root->next->data<<endl;
        }
        else
        {
            cout<<endl;
        }
        preorder(root->left);
        preorder(root->right);
    }
}
void postorder(struct node* root)
{
    if(root)
    {
        postorder(root->left);
        postorder(root->right);
        cout<<root->data<<" ";
        if(root->next)
        {
            cout<<root->next->data<<endl;
        }
        else
        {
            cout<<endl;
        }
    }
}
int main()
{
    struct node* root=createnode(1);
    root->left=createnode(2);
    root->right=createnode(3);
    root->left->right=createnode(4);
    root->left->left=createnode(5);
    root->right->right=createnode(6);
    root->right->left=createnode(7);
    root->right->right->left=createnode(8);
    //root->right->right->left->left=createnode(10);
    root->right->right->right=createnode(10);
    struct node* ptr = NULL;
    //inord_succ(root,&ptr);
    //inord_pred(root,&ptr);
    //inorder(root);
    //preord_succ(root,&ptr);
    //preord_pred(root,&ptr);
    //preorder(root);
    //postord_succ(root,&ptr);
    postord_pred(root,&ptr);
    postorder(root);
    cout<<endl;
}