TREE

#include<stdio.h>
#include<conio.h>
struct rec
{
long num;
struct rec *left;
struct rec *right;
};
struct rec *tree=NULL;
struct rec *insert(struct rec *tree,long num);
void *exchange(struct rec *tree);
struct rec *temp;
void main()
{
struct rec *tree=NULL;
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: printf("%5d\n",tree->num);exchange(tree);continue;
      case 3: puts("END");exit(0);
      }
      }while(choice!=3);
      }
      int select()
      {
      int selection;
      do
      {
      puts("Enter 1: Insert a node");
      puts("Enter 2: Exchange subtrees");
      puts("Enter 3: End");
      puts("Enter your choice");
      scanf("%d",&selection);
      if((selection<1)||(selection>3))
      {puts("Wrong choice: Try again");
       getchar();
       }
       }while((selection<1)||(selection>3));
       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;
       }
       else
       if(digit<tree->num)
       tree->left=insert(tree->left,digit);
       else if(digit>tree->num)
       tree->right=insert(tree->right,digit);
       else if(digit==tree->num)
       {puts("Duplicates Nodes: Program Exited");exit(0);
       }
       return(tree);
       }
       void *exchange(struct rec *tree)
       {
       if((tree->left->num!=0)&&(tree->right->num!=0))
       {
       temp=tree->left;
       tree->left=tree->right;
       tree->right=temp;
       printf("%5ld\n",tree->left->num);
       printf("%5ld\n",tree->right->num);
       exchange(tree->left);
       exchange(tree->right);
       }
       }

/*output of the program*/
Enter 1: Insert a node
Enter 2: Exchange subtrees
Enter 3: End
Enter your choice
1
Enter integer: To quit enter 0
1
2
3
5
4
65
0
Enter 1: Insert a node
Enter 2: Exchange subtrees
Enter 3: End
Enter your choice
2
    1
Enter 1: Insert a node
Enter 2: Exchange subtrees
Enter 3: End
Enter your choice
3