Implement-binary-tree

#include<stdio.h>
#include<stdlib.h>
struct rec
{
    long num;
    struct rec *left;
    struct rec *right;

};
struct rec *tree=NULL;
struct rec *insert(struct rec *tree,long num);
void preorder(struct rec *tree);
void inorder(struct rec *tree);
void postorder(struct rec *tree);
int select(void);
int count=1;
int main()
{
    int choice;
    long digit;
    do
     {
       choice=select();
       switch(choice)
          {
        case 1: puts("Enter integer: To quit enter 0");
            scanf("%ld",&digit);
            while(digit!=0)
                {
                tree=insert(tree,digit);

                scanf("%ld",&digit);
                }continue;
        case 2: puts("\npreorder traversing TREE");
            preorder(tree);continue;
        case 3: puts("\ninorder traversing TREEE");
            inorder(tree);continue;
        case 4: puts("\npostorder traversing TREE");
            postorder(tree);continue;
        case 5: puts("END");exit(0);
        }
    }while(choice!=5);
    return 0;
}
int select(void)
{
int selection;
    do
      {
        puts("Enter 1: Insert a node in the BT");
        puts("Enter 2: Display(preorder)the BT");
        puts("Enter 3: Display(inorder)the BT");
        puts("Enter 4: Display(postorder)the BT");
        puts("Enter 5: END");
        puts("Enter your choice");
        scanf("%d",&selection);
             if((selection<1)||(selection>5))
            {
              puts("wrong choice:Try again");
              }
       }while((selection<1)||(selection>5));
       return (selection);
}
struct rec *insert(struct rec *tree,long digit)
{
    if(tree==NULL)
      {
        tree=(struct rec *)malloc(sizeof(struct rec));
        tree->left=tree->right=NULL;
        tree->num=digit;count++;
      }
else
    if(count%2==0)
    tree->left=insert(tree->left,digit);
else
    tree->right=insert(tree->right,digit);
    return(tree);
}
void preorder(struct rec *tree)
{
    if(tree!=NULL)
      {
        printf("%12ld\n",tree->num);
        preorder(tree->left);
        preorder(tree->right);
      }
}
void inorder(struct rec *tree)
{
    if(tree!=NULL)
        {
        inorder(tree->left);
        printf("%12ld\n",tree->num);
        inorder(tree->right);
        }
}
void postorder(struct rec *tree)
{
    if(tree!=NULL)
      {
        postorder(tree->left);
        postorder(tree->right);
        printf("%12ld\n",tree->num);
      }

}