# C++ Program to Implement Double Order Traversal of a Binary Tree

C++Server Side ProgrammingProgramming

Here is a C++ Program to Implement Double Order Traversal of a Binary Tree.

In Double Order Traversal, the root of the subtree is will be traversed twice.

## Algorithm

Begin
class BST has following functions:
insert() = to insert items in the tree:
Enter the root.
Enter the value of the node, if it is greater than root then entered as right otherwise left.
doubleOrder() = To perform inorder:
If root = null
Print tree is empty
Otherwise perform:
Visit root of (sub)tree.
Visit left sub-tree.
Revisit root of (sub)tree.
Visit right sub-tree.
End

## Example Code

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

struct nod//node declaration {
int info;
struct nod *l;
struct nod *r;
}*r;

class BST {
public://declaration of functions
void insert(nod *, nod *);
void doubleOrder(nod *);
void show(nod *, int);
BST() {
r = NULL;
}
};

void BST::insert(nod *tree, nod *newnode) {
if (r == NULL) {
r = new nod;
r->info = newnode->info;
r->l = NULL;
r->r = NULL;
return;
}
if (tree->info == newnode->info) {
return;
}
if (tree->info >newnode->info) {
if (tree->l != NULL) {
insert(tree->l, newnode);
} else {
tree->l= newnode;
(tree->l)->l = NULL;
(tree->l)->r= NULL;
return;
}
} else {
if (tree->r != NULL) {
insert(tree->r, newnode);
} else {
tree->r = newnode;
(tree->r)->l= NULL;
(tree->r)->r = NULL;
return;
}
}
}

void BST::doubleOrder(nod *ptr) {
if (r == NULL) {
cout << "Tree is empty" << endl;
return;
}
if (ptr != NULL) {
cout << ptr->info << " ";
doubleOrder(ptr->l);
cout << ptr->info << " ";
doubleOrder(ptr->r);
}
}

void BST::show(nod *ptr, int level)// print the tree {
int i;
if (ptr != NULL) {
show(ptr->r, level + 1);
cout << endl;
if (ptr == r)
cout << "Root->: ";
else {
for (i = 0; i < level; i++)
cout << " ";
}
cout << ptr->info;
show(ptr->l, level + 1);
}
}

int main() {
int c, n;
BST bst;
nod *t;
while (1)//perform switch operation {
cout << "1.Insert Element " << endl;
cout << "2.Double-Order Traversal" << endl;
cout << "3.Show" << endl;
cout << "4.Quit" << endl;
cout << "Enter your choice : ";
cin >>c;
switch (c)//perform switch operation {
case 1:
t = new nod;
cout << "Enter the number to be inserted : ";
cin >>t->info;
bst.insert(r, t);
break;
case 2:
cout << "Double-Order Traversal of BST:" << endl;
bst.doubleOrder(r);
cout << endl;
break;
case 3:
cout << "Print BST:" << endl;
bst.show(r, 1);
cout << endl;
break;
case 4:
exit(1);
default:
cout << "Wrong choice" << endl;
}
}
}

## Output

1.Insert Element
2.Double-Order Traversal
3.Show
4.Quit
Enter the number to be inserted :
7
1.Insert Element
2.Double-Order Traversal
3.Show
4.Quit
Enter the number to be inserted : 6
1.Insert Element
2.Double-Order Traversal
3.Show
4.Quit
Enter the number to be inserted : 4
1.Insert Element
2.Double-Order Traversal
3.Show
4.Quit
Enter the number to be inserted : 2
1.Insert Element
2.Double-Order Traversal
3.Show
4.Quit
Enter the number to be inserted : 10
1.Insert Element
2.Double-Order Traversal
3.Show
4.Quit
Print BST:
10
Root->: 7
6
4
2
1.Insert Element
2.Double-Order Traversal
3.Show
4.Quit
Enter your choice : 4