假设一个字符串str="4*36+7+88/12^2"，C#如何直接计算出这个字符串变量str的算术值。

[zcdg909]

假设一个字符串str="4*36+7+88/12^2"，C#如何直接计算出这个字符串变量str的算术值。

[ivorstar]

搜一下“用栈实现表达式求值”。
这是数据结构和算法课程中比较基础的内容，主要思路是用两个堆栈，一个用来存储操作符，一个存储操作数，从字符串中解析出一个元素（数或运算符），通过运算符之间的优先级，控制操作符进栈出栈。出栈是指的弹出两个操作数一个运算符，然后将它们的运算结果再次入栈。直到字符串和两个栈全部为空。

[王集鹄]

public static object Eval(string AExpression)
{
    try
    {
        return new DataTable().Compute(AExpression, "");
    }
    catch
    {
        return null;
    }
}

[米菲爸爸]

楼上有个问题，乘方在C#可不是这么表示阿，四则运算楼上是对的

[wuyi8808]

那是VB的语法。

[benbenRH]

这个应该可以满足你的基本要求！！
#include <stdio.h>
#include <stdlib.h>
#define init_size 10
#define pp_size 2
int i=0;
typedef struct
{char *base;
char *top;
int size;
}optr;
typedef struct
{int *base;
int *top;
int size;
}oped;
char lable[8][8]={' ','+','-','*','/','(',')','#',
'+','>','>','<','<','<','>','>',
'-','>','>','<','<','<','>','>',
'*','>','>','>','>','<','>','>',
'/','>','>','>','>','<','>','>',
'(','<','<','<','<','<','=',' ',
')','>','>','>','>',' ','>','>',
'#','<','<','<','<','<',' ','='
};

void init_oped(oped *s)
{s->base=(int *)malloc(init_size*sizeof(int));
if(!s->base) {printf("init error!");exit(0);}
s->top=s->base;
s->size=init_size;
}

void init_optr(optr *s)
{s->base=(char *)malloc(init_size*sizeof(char));
if(!s->base) {printf("init error!");exit(0);}
s->top=s->base;
s->size=init_size;
}
void push_oped(oped *s,int e)
{if(s->top-s->base>=s->size)
{s->base=(int *)realloc(s->base,(init_size+pp_size)*sizeof(int));
if(!s->base) {printf("puss_oped error!");exit(0);}
s->top=s->base+s->size;
s->size+=pp_size;
}
*s->top=e;
s->top++;
}
void push_optr(optr *s,char e)
{if(s->top-s->base>=s->size)
{s->base=(char *)realloc(s->base,(init_size+pp_size)*sizeof(char));
if(!s->base) {printf("push_optr error!");exit(0);}
s->top=s->base+s->size;
s->size+=pp_size;
}
*s->top=e;
s->top++;
}
char pop_optr(optr *s)
{char ch;
if(s->top==s->base) {printf("optr-stack NULL!");exit(0);}
ch=*(--s->top);
return ch;
}

int pop_oped(oped *s)
{int ch;
if(s->top==s->base) {printf("oped-stack NULL!");exit(0);}
ch=*(--s->top);
return ch;
}
char gettop(optr *s)
{char ch;
if(s->top==s->base) {printf("gettop stack NULL error!");exit(0);}
ch=*(s->top-1);
return ch;
}
char precede(char x,char y)
{char ch;
int i,j;
for(i=0;i<8;i++)
if(lable[i][0]==x) break;
for(j=0;j<8;j++)
if(lable[0][j]==y) break;
ch=lable[i][j];
return ch;
}
int operate(int x,char ch,int y)
{int sum=0;
switch (ch)
{case '+':sum=x+y;break;
case '-':sum=x-y;break;
case '*':sum=x*y;break;
case '/':sum=x/y;break;
}
return sum;
}
main()
{optr *p;
oped *s;
char ch,op;
int sum=0,temp,a,b;
init_optr(p);push_optr(p,'#');
init_oped(s);
printf("\nplease enter :");
ch=getchar();
while(ch!='#'||(op=gettop(p))!='#')
{if(ch>='0'&&ch<='9')
{sum=sum*10+(ch-'0');ch=getchar();}
else {push_oped(s,sum);
sum=0;

A1: switch (precede(gettop(p),ch))
{case '<':push_optr(p,ch);ch=getchar();break;
case '=':if(ch=='#') break;
else {pop_optr(p);
ch=getchar();
break;}
case '>':{b=pop_oped(s);op=pop_optr(p);a=pop_oped(s);
temp=operate(a,op,b);
push_oped(s,temp);
goto A1;
}
}
}
}
printf("\ncomeout:%d",pop_oped(s));
}

[wuyi8808]

// SuperCalc.cs - 超级计算器

using System;
using System.Windows.Forms;
using System.CodeDom.Compiler;
using Microsoft.VisualBasic;
using System.Reflection;
using System.Text;
using System.Globalization;

namespace Skyiv
{
  class SuperCalc : Form
  {
    TextBox tbxA1;
    TextBox tbxA3;

    [STAThread]
    static void Main(string [] args)
    {
      Application.Run(new SuperCalc());
    }

    SuperCalc()
    {
      Text              = "Super Calculator";
      StartPosition     = FormStartPosition.CenterScreen;
      Width             = 300;
      Height            = 300;

      tbxA1             = new TextBox();
      tbxA1.Parent      = this;
      tbxA1.Multiline   = true;
      tbxA1.WordWrap    = false;
      tbxA1.Dock        = DockStyle.Fill;
      tbxA1.BorderStyle = BorderStyle.FixedSingle;

      Panel pnlA1       = new Panel();
      pnlA1.Parent      = this;
      pnlA1.Height      = 22;
      pnlA1.Dock        = DockStyle.Top;

      tbxA3             = new TextBox();
      tbxA3.Parent      = pnlA1;
      tbxA3.Dock        = DockStyle.Fill;
      tbxA3.BorderStyle = BorderStyle.FixedSingle;
      tbxA3.ReadOnly    = true;

      Button btnA3      = new Button();
      btnA3.Text        = "&Calculate";
      btnA3.Parent      = pnlA1;
      btnA3.Width       = 80;
      btnA3.Dock        = DockStyle.Left;
      btnA3.Click      += new EventHandler(Calc_Clicked);
    }

    void Calc_Clicked(object sender, EventArgs ea)
    {
      (sender as Control).Enabled = false;
      try
      {
        tbxA3.Text = (new Expression(tbxA1.Text)).Compute().ToString();
      }
      catch (Exception ex)
      {
        MessageBox.Show(ex.Message, "Error");
      }
      finally
      {
        (sender as Control).Enabled = true;
      }
    }
  }


  // VBExpression.cs - 动态生成数学表达式并计算其值
  // 表达式使用 Visual Baisc 语法
  // 可使用 pi、e 等常量，sin、cos、tan、log、sqrt 等函数

  sealed class Expression
  {
    object instance;
    MethodInfo method;

    public Expression(string expression)
    {
      if (expression.ToUpper(CultureInfo.InvariantCulture).IndexOf("RETURN") < 0)
      {
        expression = "Return " + expression.Replace(Environment.NewLine, " ");
      }
      string className = "Expression";
      string methodName = "Compute";
      CompilerParameters p = new CompilerParameters();
      p.GenerateInMemory = true;
      CompilerResults cr = new VBCodeProvider().CompileAssemblyFromSource
      (
        p,
        string.Format
        (
          @"Option Explicit Off
          Option Strict Off
          Imports System, System.Math, Microsoft.VisualBasic
          NotInheritable Class {0}
          Public Function {1} As Double
          {2}
          End Function
          End Class",
          className, methodName, expression
        )
      );
      if(cr.Errors.Count > 0)
      {
        string msg = "Expression(\"" + expression + "\"): \n";
        foreach (CompilerError err in cr.Errors) msg += err.ToString() + "\n";
        throw new Exception(msg);
      }
      instance = cr.CompiledAssembly.CreateInstance(className);
      method = instance.GetType().GetMethod(methodName);
    }

    public double Compute()
    {
      return (double)method.Invoke(instance, null);
    }
  }
}

[mykelly6]

很好很强大~~

[zcdg909]

难道net框架里就没有解决这个问题的类？

[Crazy_Xia]

mark
慢慢看

[wuyi8808]

[wuyi8808]

http://www.google.com/search?q=4*36%2B7%2B88%2F12%5E2&hl=zh-CN&newwindow=1&lr=&nxpt=20.39471539279207923300

(4 * 36) + 7 + (88 / (12^2)) = 151.611111

[吹风的兔子]

[Quote=引用 6 楼 wuyi8808 的回复:]

C# code
// SuperCalc.cs - 超级计算器

using System;
using System.Windows.Forms;
using System.CodeDom.Compiler;
using Microsoft.VisualBasic;
using System.Reflection;
using System.Text;
using System.Global……
[/Quote]

果然是无敌方法！！！——在效率方面：

DataTable 的 Compute() 在计算时:速度特别快！——基本的加减法几乎不消耗时间

楼主的：
Expression 的 Compute() 在计算时:速度都保持在 300 毫秒 左右！——基本的加减法也消耗这么多的时间：估计是在 编译时浪费了时间；

——但是，不容否认：Expression 真的很无敌.....