用VC编程，现在输入一个表达式(例如a+b-c*d/(e+g)+f），要求输出其结果。

Answer 1

我这里有个C++写的，参考一下吧：
#include <iostream>
#include <string.h>
using namespace std;
template <class T>
class Node
{
public:
T data;
Node<T> *next;
Node()
{
this->next = NULL;
}
Node(T data,Node<T> *next=NULL)
{
this->data = data;
this->next = next;
}
};

template <class T>
class LinkedStack
{
private:
Node<T> *top;
public:
LinkedStack();
~LinkedStack();
bool isEmpty();
void push(T x);
T pop();
T get();
};

template <class T>
LinkedStack<T>::LinkedStack()
{
top = NULL;
}

template <class T>
LinkedStack<T>::~LinkedStack()
{
Node<T> *p = top;
Node<T> *q;
while(p!=top)
{
q = p;
p = p->next;
delete p;
}
top = NULL;
}

template <class T>
bool LinkedStack<T>::isEmpty()
{
return top == NULL;
}

template <class T>
void LinkedStack<T>::push(T x)
{
top = new Node<T>(x,top);
}

template <class T>
T LinkedStack<T>::pop()
{
if(!isEmpty())
{
T x = top->data;
Node<T> *p = top;
top = top->next;
delete p;
return x;
}
throw "空栈，不能执行出栈操作";
}

template <class T>
T LinkedStack<T>::get()
{
if(!isEmpty())
{
return top->data;
}
throw "空栈，不能获得栈顶元素";
}

char * toPostfix(char *expstr)
{
LinkedStack<char> stack;
char *postfix = new char[strlen(expstr)*2];
int i=0;
int j=0;
char out ;
while(expstr[i]!='\0')
{
switch(expstr[i])
{
case'+':
case'-':
while(!stack.isEmpty()&&stack.get()!='(')
{
postfix[j++] = stack.pop();
}
stack.push(expstr[i++]);
break;
case'*':
case'/':
while(!stack.isEmpty()&&(stack.get()=='*'||stack.get()=='/'))
{
postfix[j++] = stack.pop();
}
stack.push(expstr[i++]);
break;
case'(':stack.push(expstr[i++]);
break;
case')':out = stack.pop();
while(!stack.isEmpty()&&out!='(')
{
postfix[j++] = out;
out = stack.pop();
}
i++;
break;
default:
while(expstr[i]>='0'&&expstr[i]<='9'&&expstr[i]!='\0')
{
postfix[j++] = expstr[i++];
}
postfix[j++]=' ';
break;
}
}
while(!stack.isEmpty())
{
postfix[j++]=stack.pop();
}
postfix[j]='\0';
return postfix;
}

int value(char *postfix)
{
LinkedStack<int> stack;
int i=0;
int result = 0;
while(postfix[i]!='\0')
{
if(postfix[i]>='0'&&postfix[i]<='9')
{
result = 0;
while(postfix[i]!=' ')
{
result = result*10+postfix[i++]-'0';
}
i++;
stack.push(result);
}
else
{
if(postfix[i]!=' ')
{
int y = stack.pop();
int x = stack.pop();
switch(postfix[i])
{
case'+':result = x + y;
break;
case'-':result = x - y;
break;
case'*':result = x *y;
break;
case'/':result = x / y;
break;
}
stack.push(result);
}
i++;
}
}
return stack.pop();
}

int main()
{
//char *expstr = "121+10*(52-49+20)/((35-25)*2+10)";
cout << "请输入表达式:";
//char *a ;
//cin >> *a;
char expstr[20]={0};
while(1)
{
cin>>expstr;
char *postfix = toPostfix(expstr);
cout << "expstr= "<<expstr << endl;
cout << "postfix= "<<postfix<<endl;
cout << "value= "<<value(postfix) << endl;
}
return 0;
}

Answer 2

1、先判断表达式的括号配对是否正确；
2、如果表达式正确，则将其变成后缀表达式；
3、计算。后缀表达式的值，输出。
——到数据结构书中找相应的代码。

Answer 3

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