HDU 1237

http://acm.hdu.edu.cn/showproblem.php?pid=1237

表达式计算，方法是中缀转后缀，再计算。中间处理用栈操作

讲解看http://blog.csdn.net/antineutrino/article/details/6763722

这题是简易版本的，不用处理括号

#include <iostream>

#include <cstdio>

#include <cstring>

#include <stack>



using namespace std;



int cmp(char a, char b) {

    if((a == '*' || a == '/') && (b == '+' || b == '-')) return 1;

    return 0;

}



double cal(double a, double b, char c) {

    if(c == '+') return a + b;

    if(c == '-') return a - b;

    if(c == '*') return a * b;

    if(c == '/') return a / b;

}



int main() {

    double a;

    while(~scanf("%lf", &a)) {

        char c;

        c = getchar();

        stack <char> s1;

        stack <double> s2;

        if(!a && c=='\n') break;

        s2.push(a);

        c = getchar(); 

        while(~scanf("%lf", &a)) {

            if(s1.empty()) {

                s1.push(c);

            }

            else {

                if(cmp(c, s1.top())) s1.push(c);

                else {

                    while(1) {

                        double t1 = s2.top();

                        s2.pop();

                        double t2 = s2.top();

                        s2.pop();

                        char t3 = s1.top();

                        s1.pop();

                        double t4 = cal(t2, t1, t3);

                        s2.push(t4);

                        if(s1.empty() || cmp(c, s1.top())) {

                            s1.push(c);

                            break;

                        }

                    }

                }

            }

            s2.push(a);

            if(getchar() == '\n') break;

            c = getchar();

        }

        while(!s1.empty()) {

            double t1 = s2.top();

            s2.pop();

            double t2 = s2.top();

            s2.pop();

            char t3 = s1.top();

            s1.pop();

            double t4 = cal(t2, t1, t3);

            s2.push(t4);

        }

        printf("%.2lf\n", s2.top());

    }

    return 0;

}

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