简单计算器

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

#include <iostream>
#include <cstdio>
#include <cstring>
#include <stack>
using namespace std;

int main()
{
  //freopen("test.txt", "r", stdin);
  char str, c;
  double a, b;
  stack <double> num;
  while (scanf("%lf", &a) != EOF)
  {
    while (!num.empty())
      num.pop();
    c = getchar();
    if (c == '\n' && a == 0)
      break;
    num.push(a);
    scanf("%c", &c);
    while (scanf("%lf", &b))
    {
      if (c == '*')                //优先级高，取数，计算
      {
        a = num.top();
        num.pop();
        num.push(a * b);
      }
      else if (c == '/')           //同上
      {
        a = num.top();
        num.pop();
        num.push(a / b);
      }
      else if (c == '+')           //优先级低，先存入栈
        num.push(b);
      else if (c == '-')          //减法变成加上那个数的负
        num.push(-b);

      c = getchar();
      if (c == '\n')               //结尾
        break;

      scanf("%c", &c);

      getchar();
    }
    double ans = 0.0;
    while (!num.empty())
    {
      ans += num.top();
      num.pop();
    }
    printf("%.2lf\n", ans);
  }
  return 0;
}