C :

#include<stdio.h>  
#include<stdlib.h>  
char a[505];  
double fun()  
{  
    if(scanf("%s",a)==EOF)  
        return -65535;  
    if(a[0]=='+')  
        return fun()+fun();  
    if(a[0]=='-')  
        return fun()-fun();  
    if(a[0]=='*')  
        return fun()*fun();  
    if(a[0]=='/')  
        return fun()/fun();  
    return atof(a); 
}  
int main()  
{ 
	while(1){
        double jieguo=fun(); 
		  if(jieguo>-65534)
            printf("%.2lf\n",jieguo);  
		  else 
			  break;
	}
       return 0;
   
}  

C++ :

#include <cstdio>
#include <cstdlib>
#include <stack>
#include <cstring>
using namespace std;
double val(char s, double a, double b){
    switch(s){
    case '+':
        return a+b;
    case '-':
        return a-b;
    case '*':
        return a*b;
    case '/':
        return a/b;
    }
}
int main(){
    int i,dot,len;
    char s[1200];
    double m,x,y;
    stack<double> a;
    while(gets(s)){
        for(i=strlen(s)-1;i>=0;i--){
            while(s[i-1]!=' '&&i>0) i--;
            if(s[i]<='9'&&s[i]>='0')
                a.push(atof(&s[i]));
            else{
                x=a.top();a.pop();
                y=a.top();a.pop();
                a.push(val(s[i],x,y));
            }
        }
        printf("%.2f\n",a.top());
        a.pop();
    }
    return 0;
}