首先自己百度下面两个名词

前缀表达式、后缀表达式

我们计算机 能直接计算的是后缀表达式。

前缀表达式：1+2*3+4    = 11

后缀表达式：1 2 3 *+4+ = 11

/// 
        /// 将前缀表达式转换为后缀表达式        /// 
        ///         /// 
            private string InfixToSuffix(string strInfix)        {            LinkStack ls = new LinkStack();            System.Text.StringBuilder sb = new StringBuilder(200);            string str = strInfix.Trim();            foreach(var word in str)            {                if (char.IsNumber(word))                {                    sb.Append(word);                }                else                 {                    //非数字，先加个空格。                    sb.Append(' ');                    if (word == '(')                    {                        ls.Push(word);                    }                    else if (word == ')')                    {                        while (!ls.Empty())                        {                            char ch = (char)ls.Pop();                            if (ch == '(')                            {                                break;                            }                            sb.Append(ch);                        }                    }                    else if (word == '+' || word == '-')                    {                        while(!ls.Empty())                        {                            char ch = (char)ls.Top();                            if (ch == '+' || ch == '-' || ch == '*' || ch == '/')                            {                                sb.Append((char)ls.Pop());                            }                            else if (ch == '(')                            {                                break;                            }                        }                        ls.Push(word);                    }                    else if (word == '*' || word == '/')                    {                        while (!ls.Empty())                        {                            char ch = (char)ls.Top();                            if (ch == '*' || ch == '/')                            {                                sb.Append((char)ls.Pop());                            }                            else if (ch == '+' || ch == '-' || ch == '(')                            {                                break;                            }                        }                        ls.Push(word);                    }                    else                    {                    }                }            }            while (!ls.Empty())            {                sb.Append(ls.Pop());            }            return sb.ToString();        }

下面是计算后缀表达式：

/// 
        /// 计算后缀表达式        /// 
        ///         /// 
            private int CalculateSuffix(string strSuffix)        {            LinkStack ls = new LinkStack();            int num=0;            Boolean numState = false;            foreach (var word in strSuffix)            {                if (char.IsNumber(word))                {                    numState = true;                    num = num*10+int.Parse(word.ToString());                }                else                 {                    //将数入栈                    if (numState == true)                    {                        ls.Push(num);                        num = 0;                    }                    numState=false;                    if (word != ' ')                    {                        //忽略空白                        int num2 = (int)ls.Pop(), num1 = (int)ls.Pop();                        switch(word)                        {                            case '+':                                ls.Push(num1 + num2);                                break;                            case '-':                                ls.Push(num1 - num2);                                break;                            case '*':                                ls.Push(num1 * num2);                                break;                            case '/':                                ls.Push(num1 / num2);                                break;                        }                    }                }                        }            return (int)ls.Pop();        }