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在编程应用程序过程中，有时需要字符串表达式的值。如字符串：”23+56/(102-100)*((36-24)/(8-6))”，结果=191。
根据数据结构栈的应用介绍，通过把表达式由中序式转换成后序式，再用栈来进行计算。如上述字符串表达式：”23+56/(102-100)*((36-24)/(8-6))”，转换为后序时为：”23|56|102|100|-|/|*|36|24|-|8|6|-|/|*|+”(其中字符”|”为分隔符)。
本程序代码如下：在visual .net 2003 +winxp下编译通过。
using system;
using system.drawing;
using system.collections;
using system.componentmodel;
using system.windows.forms;
using system.data;
namespace stringexpressioncalculate
{
/// <summary>
/// form1 的摘要说明。
/// </summary>
public class form1 : system.windows.forms.form
{
private system.windows.forms.textbox textbox1;
private system.windows.forms.button button1;
private system.windows.forms.textbox textbox2;
private system.windows.forms.label label1;
private system.windows.forms.label label2;
/// <summary>
/// 必需的设计器变量。
/// </summary>
private system.componentmodel.container components = null;
public form1()
{
//
// windows 窗体设计器支持所必需的
//
initializecomponent();
//
// todo: 在 initializecomponent 调用后添加任何构造函数代码
//
}
/// <summary>
/// 清理所有正在使用的资源。
/// </summary>
protected override void dispose( bool disposing )
{
if( disposing )
{
if (components != null)
{
components.dispose();
}
}
base.dispose( disposing );
}
#region windows 窗体设计器生成的代码
/// <summary>
/// 设计器支持所需的方法 – 不要使用代码编辑器修改
/// 此方法的内容。
/// </summary>
private void initializecomponent()
{
this.textbox1 = new system.windows.forms.textbox();
this.button1 = new system.windows.forms.button();
this.textbox2 = new system.windows.forms.textbox();
this.label1 = new system.windows.forms.label();
this.label2 = new system.windows.forms.label();
this.suspendlayout();
//
// textbox1
//
this.textbox1.location = new system.drawing.point(114, 33);
this.textbox1.name = “textbox1”;
this.textbox1.size = new system.drawing.size(273, 21);
this.textbox1.tabindex = 0;
this.textbox1.text = “23+56/(102-100)*((36-24)/(8-6))”;
//
// button1
//
this.button1.location = new system.drawing.point(180, 144);
this.button1.name = “button1”;
this.button1.size = new system.drawing.size(84, 27);
this.button1.tabindex = 1;
this.button1.text = “计算(&c)”;
this.button1.click += new system.eventhandler(this.button1_click);
//
// textbox2
//
this.textbox2.location = new system.drawing.point(114, 72);
this.textbox2.name = “textbox2”;
this.textbox2.size = new system.drawing.size(273, 21);
this.textbox2.tabindex = 2;
this.textbox2.text = “”;
//
// label1
//
this.label1.autosize = true;
this.label1.location = new system.drawing.point(48, 36);
this.label1.name = “label1”;
this.label1.size = new system.drawing.size(54, 17);
this.label1.tabindex = 3;
this.label1.text = “字符串：”;
//
// label2
//
this.label2.autosize = true;
this.label2.location = new system.drawing.point(39, 75);
this.label2.name = “label2”;
this.label2.size = new system.drawing.size(66, 17);
this.label2.tabindex = 3;
this.label2.text = “计算结果：”;
//
// form1
//
this.autoscalebasesize = new system.drawing.size(6, 14);
this.clientsize = new system.drawing.size(442, 221);
this.controls.add(this.label1);
this.controls.add(this.textbox2);
this.controls.add(this.button1);
this.controls.add(this.textbox1);
this.controls.add(this.label2);
this.name = “form1”;
this.text = “form1”;
this.resumelayout(false);
}
#endregion
/// <summary>
/// 应用程序的主入口点。
/// </summary>
[stathread]
static void main()
{
application.run(new form1());
}
private void button1_click(object sender, system.eventargs e)
{
textbox2.text = calculateparenthesesexpression(textbox1.text.tostring());
}
//中序转换成后序表达式再计算
// 如：23+56/(102-100)*((36-24)/(8-6))
// 转换成：23|56|102|100|-|/|*|36|24|-|8|6|-|/|*|+”
//以便利用栈的方式都进行计算。
private string calculateparenthesesexpression(string expression)
{
arraylist operatorlist = new arraylist();
string operator1;
string expressionstring = “”;
string operand3;
expression = expression.replace(” “,””);
while(expression.length > 0)
{
operand3 = “”;
//取数字处理
if(char.isnumber(expression[0]))
{
while(char.isnumber(expression[0]))
{
operand3 += expression[0].tostring() ;
expression = expression.substring(1);
if(expression == “”)break;
}
expressionstring += operand3 + “|”;
}
//取“c”处理
if(expression.length >0 && expression[0].tostring() == “(“)
{
operatorlist.add(“(“);
expression = expression.substring(1);
}
//取“)”处理
operand3 = “”;
if(expression.length >0 && expression[0].tostring() == “)”)
{
do
{
if(operatorlist[operatorlist.count -1].tostring() != “(“)
{
operand3 += operatorlist[operatorlist.count -1].tostring() + “|” ;
operatorlist.removeat(operatorlist.count – 1) ;
}
else
{
operatorlist.removeat(operatorlist.count – 1) ;
break;
}
}while(true);
expressionstring += operand3;
expression = expression.substring(1);
}
//取运算符号处理
operand3 = “”;
if(expression.length >0 && (expression[0].tostring() == “*” || expression[0].tostring() == “/” || expression[0].tostring() == “+” || expression[0].tostring() == “-“))
{
operator1 = expression[0].tostring();
if(operatorlist.count>0)
{
if(operatorlist[operatorlist.count -1].tostring() == “(” || verifyoperatorpriority(operator1,operatorlist[operatorlist.count – 1].tostring()))
{
operatorlist.add(operator1);
}
else
{
operand3 += operatorlist[operatorlist.count – 1].tostring() + “|”;
operatorlist.removeat(operatorlist.count – 1);
operatorlist.add(operator1);
expressionstring += operand3 ;
}
}
else
{
operatorlist.add(operator1);
}
expression = expression.substring(1);
}
}
operand3 = “”;
while(operatorlist.count != 0)
{
operand3 += operatorlist[operatorlist.count -1].tostring () + “|”;
operatorlist.removeat(operatorlist.count -1);
}
expressionstring += operand3.substring(0, operand3.length -1); ;
return calculateparenthesesexpressionex(expressionstring);
}
// 第二步:把转换成后序表达的式子计算
//23|56|102|100|-|/|*|36|24|-|8|6|-|/|*|+”
private string calculateparenthesesexpressionex(string expression)
{
//定义两个栈
arraylist operandlist =new arraylist();
float operand1;
float operand2;
string[] operand3;
expression = expression.replace(” “,””);
operand3 = expression.split(convert.tochar(“|”));
for(int i = 0;i < operand3.length;i++)
{
if(char.isnumber(operand3[i],0))
{
operandlist.add( operand3[i].tostring());
}
else
{
//两个操作数退栈和一个操作符退栈计算
operand2 =(float)convert.todouble(operandlist[operandlist.count-1]);
operandlist.removeat(operandlist.count-1);
operand1 =(float)convert.todouble(operandlist[operandlist.count-1]);
operandlist.removeat(operandlist.count-1);
operandlist.add(calculate(operand1,operand2,operand3[i]).tostring()) ;
}
}
return operandlist[0].tostring();
}
//判断两个运算符优先级别
private bool verifyoperatorpriority(string operator1,string operator2)
{
if(operator1==”*” && operator2 ==”+”)
return true;
else if(operator1==”*” && operator2 ==”-“)
return true;
else if(operator1==”/” && operator2 ==”+”)
return true;
else if(operator1==”/” && operator2 ==”-“)
return true;
else
return false;
}
//计算
private float calculate(float operand1, float operand2,string operator2)
{
switch(operator2)
{
case “*”:
operand1 *= operand2;
break;
case “/”:
operand1 /= operand2;
break;
case “+”:
operand1 += operand2;
break;
case “-“:
operand1 -= operand2;
break;
default:
break;
}
return operand1;
}
}
}
