//输入的时候加不加空格都行,因为是前缀表达式.//但是输出中应该要加空格,因为有可能几个数字是挨在一起的情况.//has not complete the `to_prifix`, because i do not know how to do it.#include 
       
        #include 
        
         #include 
         
          #include 
          
           using namespace std;class Compute{public:    Compute(string infix_);    int Cal();    string Prefix() { return prefix; }    string Postfix() { return postfix; }private:    string prefix;    string infix;    string postfix;private:    void to_postfix();    int cal(int n1, int n2, char c);    int compare_priory(char x, char y);};Compute::Compute(string infix_) : infix(infix_){    to_postfix();}int Compute::cal(int n1, int n2, char c){    switch (c){    case '+': return n1 + n2;    case '-': return n1 - n2;    case '*': return n1 * n2;    case '/': return n1 / n2;    }}int Compute::compare_priory(char x, char y){    if (x == '*' || x == '/') return 1;       else if ((x == '+' || x == '-') && (y == '+' || y == '-')) return 1;       else return 0;}void Compute::to_postfix(){    stack
           
             optr;    int len = infix.length();    int i;    for (i = 0; i < len; i++){        if (infix[i] == ' ') {            continue;        } else if (isdigit(infix[i])){            if (i > 0 && (!isdigit(infix[i-1]))){                postfix.push_back(' ');                postfix.push_back(infix[i]);            }else                 postfix.push_back(infix[i]);        } else {            if (optr.empty() || compare_priory(infix[i], optr.top())){                optr.push(infix[i]);            }else {                while (!optr.empty() && compare_priory(optr.top(), infix[i])){                    postfix.push_back(' ');                    postfix.push_back(optr.top());                    postfix.push_back(' ');                    optr.pop();                }                optr.push(infix[i]);            }        }    }    while (!optr.empty()){        postfix.push_back(' ');        postfix.push_back(optr.top());        postfix.push_back(' ');        optr.pop();    }    if (postfix.back() == ' ') postfix.pop_back();}int Compute::Cal(){    int len = postfix.length();    if (len == 0) return 0;    stack
            
              s; int i; int nu = 0; for (i = 0; i < len; i ++){ nu = 0; if (postfix[i] == ' ') continue; else if (isdigit(postfix[i])){ if (i > 0 && isdigit(postfix[i-1]) && !s.empty()){ nu = s.top(); nu = nu * 10 + postfix[i] - '0'; s.pop(); s.push(nu); }else s.push(postfix[i] - '0'); }else{ int n1 = s.top(); s.pop(); int n2 = s.top(); s.pop(); s.push(cal(n2, n1, postfix[i])); } } return s.top();} int main(){ Compute c("12 * 3 + 24 * 35 / 5 - 46"); cout << c.Postfix() << endl; cout << "the result is " << c.Cal() << endl; return 0;}