程序代码：

#include<stdio.h>
#include<string.h>
#include<stdlib.h>

struct tree
{
  char* p_word;
  int count;
  struct tree* left;
  struct tree* right;
};

int main()
{
  void output_tree(struct tree*);
  void input_tree(struct tree*,char*);
  struct tree* root=NULL;
  //input
  char* p=malloc(sizeof(char)*20);
  setbuf(stdin,NULL);
  scanf("%s",p);
  while((*p)!='0')
    {
      input_tree(root,p);
      setbuf(stdin,NULL);
      p=malloc(20*sizeof(char));
      scanf("%s",p);
    }
  //output
  output_tree(root);
}

void input_tree(struct tree* root,char* p)
{
  if(root==NULL)
    {
      root=malloc(sizeof(struct tree));
      root->p_word=p;
      root->count=1;
      root->left=root->right=NULL;
    }
  else if(strcmp(p,root->p_word)==0)
    root->count++;
  else if(strcmp(p,root->p_word)<0)
    input_tree(root->left,p);
  else if(strcmp(p,root->p_word)>0)
    input_tree(root->right,p);
}

void output_tree(struct tree* root)
{
  if(root->left!=NULL)
    output_tree(root->left);
  if(root!=NULL)
    printf("%s:%d\n",root->p_word,root->count);
  if(root->right!=NULL)
    output_tree(root->right);
}