Binary tree | Data Structures

# include<stdio.h>
# include <conio.h>
# include <malloc.h>

struct node
{
struct node *left;
int data;
struct node *right;
}     ;

void main()
{
void insert(struct node **,int);
void inorder(struct node *);
void postorder(struct node *);
void preorder(struct node *);
struct node *ptr;
int will,i,num;
ptr = NULL;
ptr->data=NULL;
clrscr();

printf("
Enter the number of terms you want to add to the tree.
");
scanf("%d",&will);

/* Getting Input */
for(i=0;i<will;i++)
    {
    printf("
Enter the item");
    scanf("%d",&num);
    insert(&ptr,num);
    }

getch();
printf("

        INORDER TRAVERSAL

");
inorder(ptr);
getch();
printf("

        PREORDER TRAVERSAL

");
preorder(ptr);
getch();
printf("

        POSTORDER TRAVERSAL

");
postorder(ptr);
getch();
}



void insert(struct node  **p,int num)
{


if((*p)==NULL)
{       printf("
Leaf node created.");
    (*p)=malloc(sizeof(struct node));
    (*p)->left = NULL;
    (*p)->right = NULL;
    (*p)->data = num;
    return;
}
else
{       if(num==(*p)->data)
        {
        printf("

        REPEATED ENTRY ERROR
        VALUE REJECTED

");
        return;
        }
    if(num<(*p)->data)
        {
            printf("
Directed to left link.");
            insert(&((*p)->left),num);
        }
    else
        {
        printf("
Directed to right link.");
        insert(&((*p)->right),num);
        }
}
return;
}


void inorder(struct node *p)
{
    if(p!=NULL)
        {
        inorder(p->left);
        printf("
Data :%d",p->data);
        inorder(p->right);
        }
    else
        return;
}


void preorder(struct node *p)
{
    if(p!=NULL)
        {
        printf("
Data :%d",p->data);
        preorder(p->left);
        preorder(p->right);
        }
    else
        return;
}


void postorder(struct node *p)
{
    if(p!=NULL)
        {
        postorder(p->left);
        postorder(p->right);
        printf("
Data :%d",p->data);
        }
    else
        return;
}