1.遍歷時要注意判斷遞歸結束的條件if（T）

2.臨時節點變量創建是否成功判斷

#include <iostream>#include <stdlib.h>#include <stdio.h>using namespace std;typedef struct btnode{char data;struct btnode *lchild;struct btnode *rchild;}btnode;void addbitree(btnode *T , btnode *p);void PReorder(btnode *T);void inorder(btnode *T);void postorder(btnode *T);int main(){btnode *root,*p;cout << "please input data(use space reprent the end)" <<endl;char ch;cin >> ch;root = NULL;while(ch != ' '){// cout << ch <<endl;if(p = (btnode *)malloc(sizeof(btnode))){  //2.臨時節點變量創建是否成功判斷p->data = ch;p->lchild = NULL;p->rchild = NULL;}else{cout << "error" <<endl;exit(0);}if(root == NULL){root = p;}else{addbitree(root , p);}ch = getchar();//cin不能識別空格，tab或者enter}cout << "preorder " <<endl;preorder(root);cout << "ineorder " <<endl;inorder(root);cout << "posteorder " <<endl;postorder(root);return 0;}void addbitree(btnode *T, btnode *p){if(((p->data) <= (T->data))&&(T->lchild)==NULL ){T->lchild = p;}else if((p->data <=(T->data))&&(T->lchild)!=NULL){addbitree(T->lchild,p);}else if((T->rchild)==NULL){T->rchild = p;}elseaddbitree(T->rchild,p);cout << p->data <<endl;}void preorder(btnode *T){if(T){  //遍歷時要注意判斷遞歸結束的條件if（T）cout << T->data <<" ";preorder(T->lchild);preorder(T->rchild);}}void inorder(btnode *T){if(T){inorder(T->lchild);cout << T->data <<" ";inorder(T->rchild);}}void postorder(btnode *T){if(T){postorder(T->lchild);postorder(T->rchild);cout << T->data <<" ";}}