Binary Tree in C

#include <stdlib.h>

#include <stdio.h>

struct tree {

  char info;

  struct tree *left;

  struct tree *right;

};

struct tree *root; /* first node in tree */

struct tree *stree(struct tree *root,

                   struct tree *r, char info);

void print_tree(struct tree *root, int l);

int main(void)

{

  char s[80];

  root = NULL;  /* initialize the root */

  do {

    printf("Enter a letter: ");

    gets(s);

    root = stree(root, root, *s);

  } while(*s);

  print_tree(root, 0);

  return 0;

}

struct tree *stree(

  struct tree *root,

  struct tree *r,

  char info)

{

  if(!r) {

    r = (struct tree *) malloc(sizeof(struct tree));

    if(!r) {

      printf("Out of Memory\n");

      exit(0);

    }

    r->left = NULL;

    r->right = NULL;

    r->info = info;

    if(!root) return r; /* first entry */

    if(info < root->info) root->left = r;

    else root->right = r;

    return r;

  }

  if(info < r->info)

    stree(r, r->left, info);

  else

    stree(r, r->right, info);

  return root;

}

void print_tree(struct tree *r, int l)

{

  int i;

  if(!r) return;

  print_tree(r->right, l+1);

  for(i=0; i<l; ++i) printf(" ");

  printf("%c\n", r->info);

  print_tree(r->left, l+1);

}