利用二叉树计算表达式值

#include<stdio.h>
#include<iostream>
#include<cctype>
#include<stack>
#include<stdlib.h>
using namespace std;
//定义树节点 
struct TNode
{
	char cha;
	struct TNode *lchild,*rchild;
};
//定义树根 最顶树根 
TNode * Tree;
char compare(char a, char b)
{
    int i, j;
    char pre[7][7] =                        
    {	//定义运算符之间的优先级
        {'>','>','<','<','<','>','>'},
        {'>','>','<','<','<','>','>'},
        {'>','>','>','>','<','>','>'},
        {'>','>','>','>','<','>','>'},
        {'<','<','<','<','<','=','0'},
        {'>','>','>','>','0','>','>'},
        {'<','<','<','<','<','0','='},
    };
    switch(a)
    {
    case '+':
        i = 0;
        break;
    case '-':
        i = 1;
        break;
    case '*':
        i = 2;
        break;
    case '/':
        i = 3;
        break;
    case '(':
        i = 4;
        break;
    case ')':
        i = 5;
        break;
    case '#':
        i = 6;
        break;
    }
    switch(b)
    {
    case '+':
        j = 0;
        break;
    case '-':
        j = 1;
        break;
    case '*':
        j = 2;
        break;
    case '/':
        j = 3;
        break;
    case '(':
        j = 4;
        break;
    case ')':
        j = 5;
        break;
    case '#':
        j = 6;
        break;
    default:
        printf("表达式要以#结尾！！！\n");
        exit(1);
    }
    return pre[i][j];
}
//创建树节点 
TNode * CreatNode(TNode *T,TNode *l,TNode *r,char ch)
{
	T->cha = ch;
	T->lchild = l;
	T->rchild = r;
	return T;
}
//读入表达式 
void init_EXPT()
{
	stack<TNode *> EXPT;
	stack<char> OPTR;
	OPTR.push('#');
	char ch;
	cin>>ch;
	while(ch!='#'||OPTR.top()!='#')
	{
		if(isdigit(ch))
		{
			TNode *T ;
			T = (TNode *)malloc(sizeof(TNode));
			Tree = CreatNode(T,NULL,NULL,ch);
			EXPT.push(Tree);
			cin>>ch;
		}
		if(!isdigit(ch))
		{
			if(OPTR.empty())
				OPTR.push(ch);
			else
			{
				char top;
				top = OPTR.top();
				switch(compare(top,ch))
				{
					case '<':
						{
							OPTR.push(ch);
							cin>>ch;
							break;
						}
					case '>':
						{
							TNode * T ,*a,*b;
							T = (TNode *)malloc(sizeof(TNode));
							char theta = OPTR.top();OPTR.pop();
							b = EXPT.top();EXPT.pop();
							a = EXPT.top();EXPT.pop();
							Tree = CreatNode(T,a,b,theta);
							EXPT.push(Tree);
							break;
						}
					case '=':
						{
							OPTR.pop();
							cin>>ch;
							break;
						}
				}
			}
		}
	}
}
//计算表达式 
float getvalue(char optr,float a,float b)
{
	float result ;
	switch(optr)
	{
		case '+':
			{
				result = (float)a+(float)b;
				break;
			}
		case '-':
			{
				result = (float)a-(float)b;
				break;
			}
		case '*':
			{
				result = (float)a*(float)b;
				break;
			}
		case '/':
			{
				result = (float)a/(float)b;
				break;
			}
	}
	return result;
}
float calculate(TNode *T)
{
	float lvalue,rvalue;
	lvalue = rvalue = 0;
	if(T->lchild==NULL&&T->rchild==NULL)
		return T->cha - '0';
	else
	{
		lvalue = (float)calculate(T->lchild);
		rvalue = (float)calculate(T->rchild);
		return getvalue(T->cha,lvalue,rvalue);
	}
}

int main() 
{
	float result;
    cout<<"请输入表达式并以'#'结尾(例如：7/(5+2)#)："<<endl;
	init_EXPT();
	
	result = calculate(Tree);
	cout<<result<<endl;
	return 0;
}