一个表达式计算器的局部代码（涉及异常 和 处理运算符号的思路）

 1 namespace Calculator
 2 {
 3     /// <summary>
 4     /// Calculator 的摘要说明。
 5     /// </summary>
 6     public class Calculator
 7     {
 8         public Calculator()
 9         {
             //
             // TODO: 在此处添加构造函数逻辑
             //
         }
 
         public double Calculat(string Expression)
         {
             double result = 0d;
  
             //去掉空格
             Expression = Expression.Replace(" ", "");
 
             //运算符超过一个，抛出错误
             if(Expression.Replace("+", "").Replace("-","").Replace("X", "").Replace("/", "").Length 
                 < Expression.Length - 1)
             {
                 throw new ApplicationException("运算符个数不能超过一个");
             }
             //如果没有运算符，尝试转换为数字
             else if(Expression.Replace("+", "").Replace("-","").Replace("X", "").Replace("/", "").Length 
                 == Expression.Length)
             {
 
                 //不能转换为数字，抛出错误
                 try
                 {
                     result = double.Parse(Expression);
                 }
                 catch
                 {
                     throw new ApplicationException("输入数字错误。");
                 }
             }
             //只有一个运算符的情况
             else
             {
                 char[] splitChar = {'+', '-', 'X', '/'};
 
                 //用加、减、乘、除符号把字符串分成两短
                 string[] number = Expression.Split(splitChar);
                 
                 //分别进行加、减、乘、除运算
                 if(Expression.IndexOf("+") > 0)
                 {
                     result = double.Parse(number[0]) + double.Parse(number[1]);
                 }
                 else if(Expression.IndexOf("-") > 0)
                 {
                     result = double.Parse(number[0]) - double.Parse(number[1]);
                 }
                 else if(Expression.IndexOf("X") > 0)
                 {
                     result = double.Parse(number[0]) * double.Parse(number[1]);
                 }
                 else
                 {
                     //除数是零，抛出错误
                     if(Convert.ToDouble(number[1]) == 0d)
                     {
                         throw new DivideByZeroException();
                     }
                     result = double.Parse(number[0]) / double.Parse(number[1]);
                 }    
             }
             return result;
         }
     }
 }