后缀表达式的特点如下：
1、后缀表达式的操作数与中缀表达式的操作数先后次序相同，而运算符的先后次序不同。
2、后缀表达式中没有括号，而且运算符没有优先级。
3、后缀表达式计算过程严格按照从左到右的顺序进行。
例如：
算术表达式a+(b-c)*d的后缀式是：abc-d*+
在输入的时候出了问题:
string s;
cin>>s; 不能输入空格
所以要用getline
getline(cin,s);
头文件 string 或者istream
#include<iostream>
#include<string>
#include<istream>
#include<cstring>
#include<iomanip>
using namespace std;
typedef struct StackNode *LStack;
struct StackNode {
double nu;
LStack next;
};
void Init(LStack &s)
{
s = new StackNode;
s = NULL;
}
void Pushnu(LStack &s, double c)
{
LStack p = new StackNode;
p->nu = c;
p->next = s;
s = p;
}
void Pop(LStack &s)
{
LStack p;
p = s;
if (!s->next)
s = NULL;
else
s = s->next;
delete p;
}
double GetTopnu(LStack &s)
{
return s->nu;
}
int main()
{
string s;
s = "";
cout << setiosflags(ios::fixed) << setprecision(2);
while (s != "=")
{
getline(cin, s);
char *ptr;
int length = 0;
LStack p;//s1是数字，s2是运算符
Init(p);
for (int i = 0; i <s.size(); i++)
{
if (s[i] >= '0'&&s[i] <= '9')
{
Pushnu(p, s[i] - 48);
}
else
if (s[i] == '+')
{
double a, b;
a = GetTopnu(p);
Pop(p);
b = GetTopnu(p);
Pop(p);
double c;
c = a + b;
Pushnu(p, c);
}
else
{
if (s[i] == '-')
{
double a, b;
a = GetTopnu(p);
Pop(p);
b = GetTopnu(p);
Pop(p);
double c;
c = b - a;
Pushnu(p, c);
}
else
if (s[i] == '*')
{
double a, b;
a = GetTopnu(p);
Pop(p);
b = GetTopnu(p);
Pop(p);
double c;
c = b * a;
Pushnu(p, c);
}
else
{
if (s[i] == '/')
{
double a, b;
a = GetTopnu(p);
Pop(p);
b = GetTopnu(p);
Pop(p);
double c;
c = b / a;
Pushnu(p, c);
}
else
if (s[i] == '=')
break;
else
if (s[i] == ' ')
{
continue;
}
}
}
}
if (s == "=")
return 0;
cout << p->nu << endl;
}
return 0;
}