C语言二叉树，一个猜动物的小游戏

1. 此项目用到的知识点: 二叉树， struct，文件读写。

2. 其中最复杂的地方是：复制一个指针的内容，参考：https://stackoverflow.com/questions/39938648/copy-one-pointer-content-to-another

1. 头文件 "node_utils.h"


#define BOOL int
#define TRUE 1
#define FALSE 0//This is the NODE type definition.
//The field question_or_animal contains
//either an animal name if the node is a leaf
//or a question used to descend into the tree.
//The left child represents the node to descend
//to if the answer to the question is "yes", the
//right child represents the node to descend to
//if the answer is "no".typedef struct node {char question_or_animal[200];struct node *left;struct node *right;
} NODE;//This reads a line from the standard input.
//It returns true if a line was actually read.
//It returns false if end-of-file was encountered
//before any data could be read.BOOL read_line(char *p);//Recursively performs a pre-order traversal of the
//tree starting at node p, printing the question_or_animal field to
//the file specified by the file pointer.void write_tree(NODE *p, FILE *f);//Reads the file specified by the file pointer and 
//creates a tree based on the contents of the file.
//Returns a pointer to the root node of the tree.NODE *read_tree(FILE *f);

2. 二叉树节点相关的函数 node_utils.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "node_utils.h"#define BOOL int
#define TRUE 1
#define FALSE 0BOOL read_line(char *p)
{char c = getchar();if (c == EOF)return FALSE;while ((c == '\n') || (c == ' ') || (c == '\t')) //ignore leading whitespacec = getchar();while (c != '\n') {*p++ = c;c = getchar();}*p = 0;return TRUE;
}void write_tree(NODE *p, FILE *f)
{if (p == NULL)fprintf(f,"NULL\n");else {fprintf(f,"%s\n", p->question_or_animal);write_tree(p->left,f);write_tree(p->right,f);}
}NODE *read_tree(FILE *f)
{char s[200];int i;NODE *n;char c;//attempt to read the first character of the linec = getc(f);//if end-of-file has been reached, then it means//that the input wasn't structured correctly.if (c == EOF) {printf("Error: Wrong number of entries in file\n");exit(1);}i = 0;for(i=0; (c != EOF) && (c != '\n'); i++) {s[i] = c;c = getc(f);}s[i] = 0;if(!strcmp(s,"NULL"))return NULL;n = (NODE *) malloc(sizeof(NODE));strcpy(n->question_or_animal, s);n->left = read_tree(f);n->right = read_tree(f);return n;
}

3. 主函数 animals.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "node_utils.h"#define BOOL int
#define TRUE 1
#define FALSE 0NODE *root = NULL;BOOL yes_response() {char response[10];while (TRUE) {fgets(response, 11, stdin);response[strcspn(response, "\n")] = 0;  // remove leading newlineif (strcasecmp(response, "yes") == 0) {return TRUE;} else if (strcasecmp(response, "y") == 0) {return TRUE;} else if (strcasecmp(response, "no") == 0) {return FALSE;} else if (strcasecmp(response, "n") == 0) {return FALSE;} else {printf("You answered neither yes nor no!\n");}}
}NODE *new_node(char *s) {NODE *newNode = (NODE *) malloc(sizeof(NODE));char *s2;s2 = malloc(sizeof(char) * (strlen(s) + 1));strcpy(s2, s);strcpy(newNode->question_or_animal, s2);newNode->left = NULL;newNode->right = NULL;free(s2);return newNode;
}void guess_animal() {if (!root) {printf("What animal were you thinking of? > ");char *animal_name;fgets(animal_name, 200, stdin);animal_name[strcspn(animal_name, "\n")] = 0;  // remove leading newlineroot = new_node(animal_name);} else {NODE *current_node = new_node(root->question_or_animal);*current_node = *root;while (current_node->left && current_node->right) {printf("%s (yes/no) > ", current_node->question_or_animal);if (yes_response()) {current_node = current_node->left;} else {current_node = current_node->right;}}printf("I'm guessing: %s\n", current_node->question_or_animal);printf("Am I right? >");if (yes_response()) {printf("I win ! \n");return;}// ask 3 questionsprintf("\noops.   What animal were you thinking of? > ");char new_animal_name[200];fgets(new_animal_name, 200, stdin);new_animal_name[strcspn(new_animal_name, "\n")] = 0;  // remove leading newlineprintf("Enter a yes/no question to distinguish a %s and a %s > ", new_animal_name,current_node->question_or_animal);char new_question[200];fgets(new_question, 200, stdin);new_question[strcspn(new_question, "\n")] = 0;  // remove leading newlineprintf("What is the answer of a %s (yes or no) > ", new_animal_name);BOOL yes_no_to_new_question = yes_response();// create 2 nodeschar *new_animal_name_ptr = new_animal_name;NODE *newAnimalNode = new_node(new_animal_name_ptr);     // yesNODE *oldAnimalNode = new_node(current_node->question_or_animal);// set relationschar *question;question = malloc(sizeof(char) * (strlen(new_question) + 1));strcpy(question, new_question);strcpy(current_node->question_or_animal, question);if (yes_no_to_new_question) {current_node->left = newAnimalNode;current_node->right = oldAnimalNode;} else {current_node->left = oldAnimalNode;current_node->right = newAnimalNode;}if (root->left && root->right) {if (yes_no_to_new_question) {root->left = current_node;} else {root->right = current_node;}} else {*root = *current_node;}free(question);}
}//This code is complete. Just add comments where indicated.int main() {int i;BOOL done = FALSE;//insert comment here: read a data file "data.dat", assign to a pointerFILE *datafile = fopen("data.dat", "r");if (datafile == NULL) {printf("data.dat not found\n");exit(1);}//insert comment here: read the backup file.FILE *backupfile = fopen("data.dat.bak", "w");//insert comment here: find the root of a binary treeroot = read_tree(datafile);//call write_tree() to write the initial tree to the//backup file (i.e. to back up the tree data)write_tree(root, backupfile);//close both files (for now)fclose(backupfile);fclose(datafile);printf("Welcome to the animal guessing game (like 20 questions).\n");do {printf("\nThink of an animal...\n");guess_animal();  // insert comment here: run the main gameprintf("\nDo you want to play again? (yes/no) >");} while (yes_response());  // keep ask user input if the response always is yes//now open the "data.dat" file for writingdatafile = fopen("data.dat", "w");//insert comment:// call write_tree() to write the full binary tree to a data file (data.dat).// this will overwrite the original content.write_tree(root, datafile);//close the data.dat filefclose(datafile);
}

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