Advanced Experiment 3-3.1 seeking prefix value of the expression (25 points)

Advanced Experiment 3-3.1 seeking prefix value of the expression (25 points)

Arithmetic expression notation prefix, infix and postfix notation representation method. A binary operator prefix expression means located before the two operands, e.g. prefix expression 2 + 3 * (7-4) +8/4 is: 2 + + * 3--74 / 84. Please design program calculates the result of the expression prefix value.

: Input format
separated by a space, *, /, and calculating the number of different objects (operand, the arithmetic sign) - input is given no more than 30 characters in a line prefix expression that contains only +.

Output format:
calculation result output prefix expression, retaining a decimal or an error message ERROR.

Sample input:
+ 2 * 3--74 / 84

Sample output:
13.0

Expression from right to left scanning, while a numeral, the number onto the stack, the face of the operator, playing a stack of two numbers, using operators calculated accordingly (the top element of the op-top thereof elements), and the result stack; repeat the process until the leftmost expression, is the value obtained by the last calculation result of the expression.

#include<iostream>
#include<stack>
using namespace std;
int main(){
    stack<int>s1;
    stack<char>s2;
    char ch;
    ch=getchar();
    while(ch!='\n'){
        if(ch!=' '){
        //cout<<"check001:"<<s2.top()<<endl;}
        s2.push(ch);}
        ch=getchar();
    }
    int x=0,y=0,z=0,a=0;
    char ca;
    while(s2.size()){
        ca=s2.top();s2.pop();
        if(ca!='+'&&ca!='-'&&ca!='*'&&ca!='/'){
            a=static_cast<int>(ca)-48;      //字符数字转化为int类型的数字
            s1.push(a);
            //cout<<"check002:"<<s1.top()<<endl;
        }
        else{
            x=s1.top();s1.pop();
            y=s1.top();s1.pop();
            if(ca=='+'){z=x+y;}
            else if(ca=='-'){z=x-y;}
            else if(ca=='*'){z=x*y;}
            else if(ca=='/'){z=x/y;}
            s1.push(z);
        }
        if(s2.empty()){
            cout<<s1.top()<<endl;//----->13
        }
    }
    return 0;
}