实现四则混合运算的代码

这是一个实现四则混合运算的代码，包括三个方法，调用时，使用compute()方法即可，这个方法可以用于动态计算。
 
代码：
         string precede(string p, string q)
       {
           switch(p)
           {
              case "+":
              case "-":
                  return ("*/(".indexof(q) != -1) ? "<":">";
              case "*":
              case "/":
                  return (q == "(") ? "<":">";
              case "(":
                  return (q == ")") ? "=":"<";
              case ")":
                  return (q == "(") ? "?":">";
              case "#":
                  return (q == "#") ? "=":"<";
           }
           return "?";
       }
 
       double operate(double a, char o, double b)
       {
           switch(o)
           {
              case '+':
                  return a + b;
              case '-':
                  return a - b;
              case '*':
                  return a * b;
              case '/':
                  return a / b;
           }
           return 0;
       }
 
       object compute(string expression)
       {
           stack narr = new stack(), oarr = new stack();
           int j = 0;
           double a = 0, b = 0;
           string w = "";
           char o;
           matchcollection arr = regex.matches(expression.replace(" ", "") + "#", @"(((?<=(^|/())-)?/d+(/./d+)?|/d)");
 
           oarr.push("#");
           w = convert.tostring(arr[j++]);
           while(!(w == "#" && convert.tostring(oarr.peek()) == "#"))
           {
              if("+-*/()#".indexof(w) != -1)
              {
                  switch(precede(oarr.peek().tostring(), w))
                  {
                     case "<":
                         oarr.push(w);
                         w = convert.tostring(arr[j++]);
                         break;
                     case "=":
                         oarr.pop();
                         w = convert.tostring(arr[j++]);
                         break;
                     case ">":
                         o = convert.tochar(oarr.pop());
                         b = convert.todouble(narr.pop());
                         a = convert.todouble(narr.pop());
                         narr.push(operate(a, o, b));
                         break;
                     default:
                         return "计算出错！";   
                  }
              }
              else
               {
                  narr.push(w);
                  w = convert.tostring(arr[j++]);
              }
           }
           return narr.pop();
       }