后缀表达式求值

   输入只含数字和运算符的后缀表达式，求其值。

 

  

#include<iostream>
#include<stack>
#include<ctype.h>
#include<math.h>
#include<string>
using namespace std;
bool issymbol(unsigned char c)
{
	if ((c== '+')||(c== '-')||(c== '*')||(c== '/')) 
		return true; 
	return false; 

}
void main()
{
	stack<int> s1;
	unsigned char ch,che;
	int a,b;
	int sum=0;
	ch=cin.get();
	while(ch!='#')
	{
		if(ch==' '||ch=='\n')
		{
			ch=cin.get();
		}
		else if(issymbol(ch))
		{
			if(!s1.empty())
			{
				a=s1.top();
				s1.pop();
			}
			if(!s1.empty())
			{
				b=s1.top();
				s1.pop();
			}
			if(ch=='+')
			{
				s1.push(a+b);
			}
			else if(ch=='-')
			{
				s1.push(b-a);
			}
			else if(ch=='*')
			{
				s1.push(a*b);
			}
			else
			{
				s1.push(b/a);
			}
			ch=cin.get();

		}
		else if(isdigit(ch))
		{
			sum=ch-48;
			ch=cin.get();
			while(isdigit(ch))
			{
				sum=sum*10+ch-48;
				ch=cin.get();
			}
			s1.push(sum);

		}
		else
			ch=cin.get();


	}
	if(!s1.empty())
		cout<<s1.top()<<endl;
}