Binary search tree program in c++

#include<iostream>

//variable to store maximum number of nodes
int complete_node=15;

//Array to store the tree
char tree[]={'\0','D','A','F','E','B','R','T','G','Q','\0','\0','V','\0','J','L'};

int get_right_child(int index)
{

    //node is not null
	//and the result must lie within the number of nodes for a complete binary
	if(tree[index]!='\0'&& ((2*index)+1)<=complete_node)
	    return(2*index)+1;
	//right child doesn't exist
	return -1;     
}
 int get_left_child(int index)
 {
 	//node is not null
 	//and the result must lie within the number of nodes for a complete binary
 	if(tree[index]!='\0' && (2*index)<=complete_node)
 	   return 2*index;
 	//left child doesn't exist
	 return -1;   
 }
 
 void preorder(int index)
 {
 	
 	//checking for valid index and null node
 	if(index>0 && tree[index]!='\0')
 	{
 		printf("%c",tree[index]);//visiting root
 		preorder(get_left_child(index));//visitingleft subtree
 		preorder(get_right_child(index));//visiting right subtree
 		
	 }
	 
 }
	 void postorder(int index)
	 {
	 	//checking for void index and null node
	 	if(index>0 && tree[index]!='\0')
	 	{
	 	
 		postorder(get_left_child(index));//visiting left subtree
 		postorder(get_right_child(index));//visiting right subtree
 		printf("%c",tree[index]);//visiting root
 		
		 }
	 }
	 void inorder(int index)
	 {
	 	//checking for valid index and null node
	 	if(index>0 && tree[index]!='\0')
	 	{
		 
	 	inorder(get_left_child(index));//visiting left subtree
	 	printf("%c",tree[index]);//visiting root
 		inorder(get_right_child(index));//visiting right subtree
    	}
		  
	 }

	 
int main()
{
	printf("Preorder:\n");
	preorder(1);
	printf("\nPostorder:\n");
	postorder(1);
	printf("\nInorder:\n");
	inorder(1);
	printf("\n");
	return 0;
}