using System;
using System.Collections;
using System.Text;
namespace ExpresstionClass
{
public class ExpresstionClass
{
public string Expresstion;//String类型表达式
public ExpresstionClass()
{
}
public ExpresstionClass(string expresstion)
{
this.Expresstion = expresstion;
}
// 判断字符串是否为数值
public bool IsNumberExp(string str)
{
bool isnumeric = false;
byte c;
if (str == null || str.Length == 0)
return false;
System.Text.ASCIIEncoding ascii = new System.Text.ASCIIEncoding();
byte[] bytestr = ascii.GetBytes(str);
for (int i = 0; i < bytestr.Length; i++)
{
c = bytestr[i];
if ((c >= 48 && c <= 57) || c == 46)
{
isnumeric = true; ;
}
else
{
if (c == 45 && bytestr .Length > 1)
{
isnumeric = true;
}
else
{
isnumeric = false;
break;
}
}
}
return isnumeric;
}
// 基本一目计算
public double account(double n1, double n2, string num_op)
{
double aresult = 0;
switch (num_op)
{
case "+":
aresult = n1 + n2;
break;
case "-":
aresult = n1 - n2;
break;
case "*":
aresult = n1 * n2;
break;
case "/":
aresult = n1 / n2;
break;
}
return aresult;
}
// 将String类型表达式转为由操作数和运算符组成的ArrayList类型表达式
public ArrayList Toexp_arraylist(string exp_str)
{
string exp_element="",expchar;
ArrayList exp_arraylist = new ArrayList();
//遍历表达式
for (int i = 0; i < exp_str.Length; i++)
{
expchar = exp_str.Substring(i, 1);
//如果该字符为数字,小数字或者负号(非运算符的减号）
if (char.IsNumber(exp_str, i) || expchar == "." || (expchar == "-" && (i == 0 || exp_str.Substring(i - 1, 1) == "(")))
{
exp_element += expchar;//存为操作数
}
else//为运算符
{
//将操作数添加到ArrayList类型表达式
if (exp_element != "")
exp_arraylist.Add(exp_element);
//将运算符添加到ArrayList类型表达式
exp_arraylist.Add(expchar);
exp_element = "";
}
}
//如果还有操作数未添加到ArrayList类型表达式,则执行添加操作
if (exp_element != "")
exp_arraylist.Add(exp_element );
return exp_arraylist;
}
//返回运算符的优先级
private int Operatororder(string op)
{
switch (op)
{
case "*":
return 3;
break;
case "/":
return 4;
break;
case "+":
return 1;
break;
case "-":
return 2;
break;
default:
return 0;
break;
}
}
private bool IsPop(string op,Stack operators)
{
if (operators.Count == 0)
{
return false;
}
else
{
if (operators.Peek().ToString() == "(" || Operatororder(op) > Operatororder(operators.Peek().ToString()))
{
return false;
}
else
{
return true;
}
}
}
//将ArrayList类型的中缀表达式转为ArrayList类型的后缀表达式
public ArrayList Toexpback_arraylist(ArrayList exp)
{
ArrayList expback_arraylist = new ArrayList();
Stack operators = new Stack();
string op;
//遍历ArrayList类型的中缀表达式
foreach (string s in exp)
{
//若为数字则添加到ArrayList类型的后缀表达式
if (IsNumberExp(s))
{
expback_arraylist.Add(s);
}
else
{
switch (s)
{
//为运算符
case "+":
case "-":
case "*":
case "/":
while (IsPop(s,operators ))
{
expback_arraylist.Add(operators .Pop ().ToString ());
}
operators.Push(s);
break;
//为开括号
case "(":
operators.Push(s);
break;
//为闭括号
case ")":
while (operators.Count !=0)
{
op = operators.Pop().ToString();
if (op != "(")
{
expback_arraylist.Add(op);
}
else
{
break;
}
}
break;
}
}
}
while (operators.Count != 0)
{
expback_arraylist.Add(operators .Pop ().ToString ());
}
return expback_arraylist;
}
//计算一个ArrayList类型的后缀表达式的值
public double ExpValue(ArrayList expback)
{
double num1,num2,result=0;
Stack num = new Stack ();
foreach (string n in expback)
{
if (IsNumberExp(n))
{
num.Push(n);
}
else
{
num2 = Convert.ToDouble(num.Pop ());
num1 = Convert.ToDouble(num.Pop ());
result = account(num1, num2, n);
num.Push(result );
}
}
return result;
}
//返回本类的表达式值
public double ExpValue()
{
ArrayList a1 = new ArrayList();
ArrayList a2 = new ArrayList();
a1 = Toexp_arraylist(Expresstion);
a2 = Toexpback_arraylist(a1);
return ExpValue(a2);
}
}
}