C++后缀表达式求值

#include <iostream>
#include <stack>
using namespace std;
int cal(int a,int b,char c){
    if(c==‘+‘)  return a+b;
    else if(c==‘-‘)  return a-b;
    else if(c==‘*‘)  return a*b;
    else if(c==‘/‘)  return a/b;
    else return 0;
}

int postcal(char* post){
    stack <int > s;
    while(*post){
        if(*post >=‘0‘&& *post<=‘9‘){
            s.push(*post);
        }
        else{
            int a = s.top()-48;
            s.pop();
            int b = s.top()-48;
            s.pop();
            int c = cal(b,a,*post);
            s.push(c+48);
        }
        post++;
    }
    return s.top()-48;
}

int main(int argc, const char * argv[]) {
    char* post = new char;
    cin>>post;
    int res = postcal(post);
    cout<<"答案是："<<res<<endl;
    return 0;
}