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利用字符串进行数值计算的有关问题

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利用字符串进行数值计算的问题
想写一个简单的计算器程序,将整个表达式输入之后再计算结果,比如1+2*5/8,然后按=时出现结果,现在有一问题,我不知道如何将这个字符串转换为表达式进行数值计算。谢谢,结题给分。

------解决方案--------------------
//先在项目中添加COM引用Microsoft Script Control 1.0
using MSScriptControl;

ScriptControl vScriptControl = new ScriptControl();
vScriptControl.Language = "JavaScript ";
Text = vScriptControl.Eval( "1+2*5/8 ").ToString();

------解决方案--------------------
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

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