栈应用——表达式求值

#include "stdafx.h"
#include <iostream>
using namespace std;
const int EXPLENGHT=20;
const int STACK_INIT_SIZE=20;
const int STACK_INCRMENT=10;
template<typename ElemType>
class Stack
{
public:
	Stack()
	{
		m_base=(ElemType*)malloc(STACK_INIT_SIZE*sizeof(ElemType));
		if(!m_base)
			exit(0);
		m_top=m_base;
		m_size=STACK_INIT_SIZE;
		m_item=0;
	}
	~Stack()
	{
		free(m_base);
		m_base=m_top=NULL;
	}
	void push(ElemType e)
	{
		if(m_top-m_base>=m_size)
		{
			m_base=(ElemType*)realloc(m_base,(m_size+STACK_INCRMENT)*sizeof(ElemType));
			if(!m_base)
				exit(0);
			m_top=m_base+m_size;
			m_size+=STACK_INCRMENT;

		}
		*(m_top)=e;
		m_top++;
		m_item++;
	}
	void pop(ElemType &e)
	{
		if(m_top==m_base)
			return;
		m_top--;
		e=*m_top;
		m_item--;

	}
	int size()
	{
		return m_size;
	}
	bool empty()
	{
		if(m_item==0)
			return true;
		else
			return false;
	}
private:
	ElemType *m_base;
	ElemType *m_top;
	int m_size;
	int m_item;
};
void ChangeExp(char *inexp,char *sufexp)//中缀转后缀
{
	int i=0;
	int j=0;
	Stack<char> stack;
	while (1)
	{
		if(inexp[i]=='\0')
		{
			while(!stack.empty())
				stack.pop(sufexp[j++]);
			sufexp[j]='\0';
			break;
		}
		char e=inexp[i++];
		if(e>='0'&&e<='9')
		{
			sufexp[j++]=e;
			continue;
		}
		if('*'==e||'/'==e||'('==e)
			stack.push(e);
		else if(')'==e)
		{
			char c=' ';
			stack.pop(c);
			while('('!=c)
			{
				sufexp[j++]=c;
				stack.pop(c);
			}
		}
		else if('+'==e||'-'==e)
		{
			char c=' ';
			while('('!=c&&!stack.empty())
			{
				stack.pop(c);
				if('('!=c)
					sufexp[j++]=c;
			}
			if('('==c)
				stack.push(c);
			stack.push(e);
		}

	}
}
int Calculate(char *exp)//计算表达式的值
{
	int i=0;
	Stack<int> stack;
	int num1;
	int num2;
	while(exp[i]!='\0')
	{
		if(exp[i]>='0'&&exp[i]<='9')
			stack.push(exp[i]-'0');
		else
		{
			stack.pop(num1);
			stack.pop(num2);
			switch(exp[i])
			{
			case '+':
				stack.push(num2+num1);
				break;
			case '-':
				stack.push(num2-num1);
				break;
			case '*':
				stack.push(num2*num1);
				break;
			case '/':
				stack.push(num2/num1);
				break;
			}
		}
		i++;
	}
	int result;
	stack.pop(result);
	return result;
}
int _tmain(int argc, _TCHAR* argv[])
{
	char inexp[EXPLENGHT];
	char sufexp[EXPLENGHT];
	cout<<"输入中缀表达式(最大长度20)："<<endl;
	cin>>inexp;
	ChangeExp(inexp,sufexp);
	cout<<"后缀表达式："<<endl;
	cout<<sufexp<<endl;
	cout<<"运算结果："<<Calculate(sufexp)<<endl;
	system("pause");
	return 0;
}