树结点

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <ctype.h>
#define MAX_LEN 5      


typedef struct node    // 结点类型定义 
{
    char optr; 
    int data;
    struct node *lchild; 
    struct node *rchild; 
}BTNode; 

BTNode *getNode(char *str,int &pos)
{
    BTNode *createTree(char *str,int &pos);
    BTNode *p = new BTNode;
    char ch = str[0]; 
    if(isdigit(ch))
    {
        int i = 0;
        char data[MAX_LEN];
        while(isdigit(ch=str[i]))
            data[i++] = ch;
        p->data = atoi(data);
        pos += i;
    }
    else if(ch =='+' || ch =='-' || ch =='*' || ch =='/')
    {
        p->optr = ch;
        pos += 1;
    }
    else if(ch =='(')
    {
        pos += 1;
        p = createTree(str+1,pos);        
    }
    else if(ch ==')')
    {
        pos += 1;
        return NULL;
    }
    else if(ch=='\0')
        return NULL;
    return p;
    
}
int getPriority(char optr)
{
    switch(optr)
    {
    case '+':
    case '-':
        return 1;
    case '*':
    case '/':
        return 2;
    }
    return 0;
}
BTNode *createTree(char *str,int &pos)
{
    int pos1 = 0;
    BTNode *lchild = getNode(str+pos1,pos1);
    BTNode *root = getNode(str+pos1,pos1);
    BTNode *rchild = getNode(str+pos1,pos1);
    root->lchild = lchild;
    root->rchild = rchild;
    
    BTNode *node;
    while((node=getNode(str+pos1,pos1)))
    {
        if(getPriority(root->optr) > getPriority(node->optr))
        {
            node->lchild=root;
            node->rchild=getNode(str+pos1,pos1);
            root = node;
        }
        else
        {
            node->lchild=root->rchild;
            root->rchild=node;
            node->rchild=getNode(str+pos1,pos1);
        }
    }
    pos += pos1;
    return root;
}
int result(BTNode *b) //计算表达式 
{ 
    int n1,n2;  
    
    switch(b->optr) 
    { 
    case'+': 
        n1=result(b->lchild);//计算左子表达式 
        n2=result(b->rchild);//计算右子表达式
        b->data=n1+n2;break; 
    case'-': 
        n1=result(b->lchild);//计算左子表达式 
        n2=result(b->rchild);//计算右子表达式
        b->data=n1-n2;break; 
    case'*': 
        n1=result(b->lchild);//计算左子表达式 
        n2=result(b->rchild);//计算右子表达式
        b->data=n1*n2;break;    
    case'/': 
        n1=result(b->lchild);//计算左子表达式 
        n2=result(b->rchild);//计算右子表达式
        b->data=n1/n2;break; 
    default:
        return b->data;
    } 
    return b->data; 
}
void main() 
{ 
    BTNode *b=NULL,*q=NULL; 
    char str[100];    //="(20+30+5)*3"; 
    printf("请输入符合要求的代数表达式："); 
    scanf("%s",str); 
    int n=0,i=0; 
    while(str[i++] != '\0') 
        n++;
    int pos = 0;
    b = createTree(str,pos);
    //  b = create(str,n); 
    printf("该表达式的值为：%d\n",result(b)); 
    int a;
    scanf("%d",&a);
}