我用while来建立一个树，不成功，帮我看看。
因为对递归不熟悉，就用while来建立一个树，不能正确显示，请帮我释疑。这棵树就是把大于10的数放到左子树上，小于或等于10的放到右子树上。
#include "stdafx.h"
#include "stdio.h"
#include "stdlib.h"
typedef int Item;
typedef struct node
{
Item item;
struct node *left;
struct node *right;
}Node;
typedef struct tree
{
Node *root;
int size;
}Tree;
void InitializeTree(Tree *ptree);
void CreateTree(Item item, Tree *ptree);
int CountTree(Tree *ptree);
void PreShowTree(Tree *ptree);
void MidShowTree(Tree *ptree);
int main(void)
{
static Tree data;
Item number;
InitializeTree(&data);
puts("Please enter the first item:(enter 'q' to quit)");
while(scanf("%d", &number) == 1)
{
while(getchar() != '\n')
{
continue;
}
CreateTree(number, &data);
puts("Please enter another item:(enter 'q' to quit)");
}
printf("There are %d items on the tree.\n", CountTree(&data));
puts("先序显示：");
PreShowTree(&data);
puts("\n中序显示：");
MidShowTree(&data);
printf("\n");
return 0;
}
void InitializeTree(Tree *ptree)
{
ptree->root = NULL;
ptree->size = 0;
}
void CreateTree(Item item, Tree *ptree)
{
Node *pnew;
pnew = (Node *)malloc(sizeof(Node));
if(pnew == NULL)
{
fprintf(stderr, "Failing to allocate memory.\n");
}
else
{
pnew->item = item;
pnew->left = NULL;
pnew->right = NULL;
if(ptree->root == NULL)
{
ptree->root = pnew;
}
else
{
if(item > 10)
{
while(ptree->root->left != NULL)
{
ptree->root = ptree->root->left;
}
ptree->root->left = pnew;
}
else
{
while(ptree->root->right != NULL)
{
ptree->root = ptree->root->right;
}
ptree->root->right = pnew;
}
}
ptree->size++;
}
}
int CountTree(Tree *ptree)
{
return ptree->size;
}
void PreShowTree(Tree *ptree)
{
if(ptree->root != NULL)
{
printf("%d ", ptree->root->item);
while(ptree->root->left != NULL)
{
ptree->root = ptree->root->left;
printf("%d ", ptree->root->item);
}
while(ptree->root->right != NULL)
{
ptree->root = ptree->root->right;
printf("%d ", ptree->root->item);
}
}
}
void MidShowTree(Tree *ptree)
{
if(ptree->root != NULL)
{
while(ptree->root->left != NULL)
{
ptree->root = ptree->root->left;
printf("%d ", ptree->root->item);
}
printf("%d ", ptree->root->item);
while(ptree->root->right != NULL)
{
ptree->root = ptree->root->right;
printf("%d ", ptree->root->item);
}
}
}
不要使用
while (条件)
更不要使用
while (组合条件)
要使用
while (1) {
if (条件1) break;
//...
if (条件2) continue;
//...
if (条件3) return;
//...
}
因为前两种写法在语言表达意思的层面上有二义性，只有第三种才忠实反映了程序流的实际情况。
典型如：
下面两段的语义都是当文件未结束时读字符
whlie (!feof(f)) {
a=fgetc(f);
//...
b=fgetc(f);//可能此时已经feof了！
//...
}
而这样写就没有问题：
whlie (1) {
a=fgetc(f);
if (feof(f)) break;
//...
b=fgetc(f);
if (feof(f)) break;
//...
}
类似的例子还可以举很多。
